Paper - The developmental history of the primates
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Hill JP. The developmental history of the primates. (1932) Phil. Trans. Roy. Soc. London B, 221:45-178. PubMed 20775204
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This historic 1932 paper by James Hill describes several early human embryos.
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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History | Historic Embryology Papers) |
The Developmental History of the Primates
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76 JAN. ‘[1, 1930]
DEVELOPMENTAL HISTORY OF THE PRIMATES.
Tm; Bnrnsn Msmcu. Joomzu.
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DEVELQPi\IEiNTAL HISTORY or THE PRIMATES.
Professor. J. P. Hill’s Croonian Lecture.
THE following is an abstract of the Croonian Lecture for 1929, on the developmental history of the primates, delivered before the Royal Society by Professor J. P. Hill, F.R.S.
Starting with the relatively simple developmental conditions met .with in the Lemuroidea, Professor Hill considered the question of how the much more specialized and modified developmental relations found in the higher primates might be supposed to have arisen as the result of adaptive specialization, involving more especially acceleration and abbreviation in the developmental processes. A broad survey of the early development and placentation in representatives of the chief divisions of the order had led to the recognition of four main stages in its evolutionary history— lemuroid, tarsioid, pithecoid, and anthropoid.
The existing lemurs, said Professor Hill, were regarded, from the developmental point of view, as remnants of that basal lemurine stock from which the higher primates took their origin. In their development they exhibited a combination of primitive features with others which wereycertainly advanced, and which foreshadowed conditions characteristic of the higher types. Primitive features were evinced in the constitution of the blastocyst and its central type of development, in the disappearance of the covering trophoblast and consequent exposure of the embryonal ectoderm, in the origin and mode of spreading of the mesoderm, in the formation of amnion by folds, and in the development of the allantois as a free vesicle. Among the advanced features might be included the relatively early establishment of a complete chorion and its direct and complete vascularization by the ingrowth into it of the allantoic vessels and the reduction of_the yolk-sac and its vessels. Their placentation was regarded as genuinely primitive, and the lecturer considered the manner in which the more specialized haemochorial type of the higher primates miglit have bee11 substituted for it.
In the tarsioid stage, as exemplified by the existing tarsius,
was to be observed the retention of certain lowiy fcat11r(‘s
characteristic of the lemuroids-——for example, the’ exposure
of the embryonal ectoderm and the (levelcpmcnt cf the
amnion by fold formation. At this stage certain developmental tendencies could be discerned which were already foreshadowed in the lemuroids—namely, the still more precocious
differentiation of the extra-embryonal mesoderm, coelom, and
chorion, and the replacement of the vesicular allantois by the
almost solid connecting stalk, all of them features in which
tarsius anticipates the pithecoids. Also present were certain
definite advances on the lemuroid, in particular the acquisition
by an early blastocyst of a direct attachment to the uterine
lining and the resulting formation of a massive discoidal
placenta of the deciduate haemochorial type.
In discussing the development of the placenta Professor Hill
showed that the trophoblast was unique, both in its histological characters and in its behaviour, and on these grounds
cencltuled that the tarsius placenta was too specialized to have
been the actual forerunner of that of the pithecoids, but would
seem to have developed along lines of its own, as a parallel
format-ion. Acceptancejof this conclusion in regard to the
placenta in no way lessened the significance of the tarsioid
phase as the more important transitional stage in the evolution
of the developmental processes of the primates. It was only
to suppose that the pithecoids took origin from
another branch of the tarsioid stock in which the attempt at the formation of a haemochorial placenta. proceeded along lines comparable with those which were found in the existing pithecoids.
Passing to a consideration of the pithecoid stage, the lecturer
said that the justification for the recognition of this stage
rested on the occurrence in the platyrrhine and ca‘.-arrhine
monkeys of certain striking resemblances in their early development, all of the nature of definite developmental advances on
the tarsioid condition. ~ In this stage the amnion no longer
developed by fold formation, since its cavity, the primitive
amniotic cavity, arose as a closed-space in the ectodermal cell mass of the very early blastocyst. The primaryattachment of
the blastocyst to the uterine wall was always effected by the
trophoblast over the embryonal pole. A second attachment was
also usually formed at the anti-embryonal pole, in which case
the placenta was bidiscoidal. The extra-embryonal mesoderm
and coelom and the mesodermal primordium of the connecting
stalk were formed even more precociously than in the tarsioid.
The extra-embryonal mesoderm (the so-called primary mesoderm
of the early human blastocyst), though homologous with that of
the tarsioid, was no longer of direct primitive streak origin,
but appeared to arise, as in hapale, as a proliferation from
the hinder margin of the shield ectoderm and the adjoining
amniotic ectoderm. The trophoblast always became clearly
distinguishable into cellular and syncytial layers. The syncytiotrophoblast exhibited erosive and destructive properties, and
had the capacity of proliferating and of penetrating more
or less -deeply into the maternal decidual tissue in the form of
an irregular network. The existence of certain well-marked
differences in the behaviour of the trophoblast and in the
structure of the placenta in the two groups of monkeys, and
the very striking similarities in the development of the placenta
in the catarrhines and the anthropoids, suggs.-sted that the
platyrrhines separated very early from the parent stem to
pursue a path of their own, while the catarrl1ine.s furnished the
stock from which the anthropoids originated.
In the anthropoid stage were grouped together anthropoid apes and man, and in this stage was to be seen the culmination of developmental adaptation so far as the primates were concerned. Though there was no knowledge about the earlicr stage in the development of the anthropoid apes, c.nough was known - thanks to the labours of Selenka and Strahl - of their later stages and placentation to justify the belief that their development conformed in all essentials to the human type, so that for the details of early anthropoid ontogeny the work of the human embryologist must be relied on.
The outstanding feature of the early human blastocyst was its
extraordinary precoc_ity., as exemplified, for example, in the
relations it very early acquired to the uterine lining, and in
the reniarkably early differentiation of its trophoblast and its
extra-embi_~_vona.l mesoder-ms It was no longer content to
undergo its development in the uterine lumen, as did the blastecysts of the lower primates, but, while still quite minute, it
burrowed its way through the uterine epithelium and implanted
itself in the very vascular subepithelial desidual tissue of the
uterus“; Therein it formed for itself a decidual cavity and
underwent its Sul)s'eQllt‘Ill development, completely embedded in
the maternal tissue. In this way the primate germ reached
the acme of its endeavour to maintain itself in the uterus and
to obtain an adequate supply of nutriment at the earliest
possible moment. It was a significant fact that just the
pithecoid blastocyst always attached itself by the embryonal
pole, so here that. pole was the first to enter, and the embryo
lay on the deep side of the blastocyst in immediate proximity
to the site of formation of the definitive placenta.
Certain features, distinctive of the anthropoids, were to be
regarded as the direct outcome of this process of interstitial
implantation, and consequently as purely secondary specializations. These included differentiation of a decidua capsularis
from the decidual tissue covering the blastocyst; formation
round the very early blastocyst of a complete enveloping
network of syncytio-trophoblast, possessing in even more marked
degree than that of the pithecoids destructive and penetrative
properties; and development from the chorion of the older
blastocyst of a more or less uniform covering of chorionic
villi. In the blastocyst itself formation of the extra-embryonal
mesoderm apparently took place at such an early period that
it. was able to fill the minute cavity of the blastocyst completely
as a delicate cellular tissue in which only later the coelomic
cavity appeared.
Apart from these adaptive specializations, the anthropoid
developed along the. lineslaid down in the catarrhine stock, and
as [a result of the atrophy of the chorionic villi originally
related to the decidua capsularis an-d the growth of those related
to the decidua basalis, formed a single discoidal placenta, the
homologue of the primary placenta of the catarrhine, and differing from that only in minor details and in the rather more individualized character of its foetal chorionic villi. Of the genetic relationship of the anthropoid apes and man, and of these to, the catarrliine stock, concluded Professor Hill, there could be
no question on embryological-grounds.
Cite this page: Hill, M.A. (2024, April 24) Embryology Paper - The developmental history of the primates. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_developmental_history_of_the_primates
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G