The Gastraea bilateralis, of which we may conceive the bilateral gastrula of the amphioxus to be a palingenetic reproduction, represented the two-sided organism of the earliest Metazoa in its simplest form.
In this we have throughout taken strict account of the distinction between palingenetic and cenogenetic phenomena.
We saw that the palingenetic form of the heart is a spindle-shaped thickening of the gut-fibre layer in the ventral wall of the head-gut.
In order to appreciate this important feature, we have distributed the embryological phenomena in two groups, palingenetic and cenogenetic.
In order to distinguish correctly between palingenetic and cenogenetic phenomena in embryology, and deduce sound conclusions in connection with stem-history, we must especially make a comparative study of the former.
We must, above all, clearly distinguish between palingenetic and cenogenetic phenomena.
In the genealogical tree of the Vertebrates this palingenetic form of segmentation has been preserved in the Amphioxus alone, all the other Vertebrates having cenogenetically modified forms of cleavage.
Moreover, in the animals in which we do not find a real palingenetic blastula the defect is clearly due to cenogenetic causes, such as the formation of food-yelk and other embryonic adaptations.
Hence I insisted from the first that the biogenetic law consists of two parts, one positive and palingenetic and the other restrictively negative and cenogenetic.
This is one of the most interesting of the palingenetic facts that prove the descent of the amniotes (including man) from the fishes.
This cenogenetic gastrocystis and the palingenetic blastula are sometimes very wrongly comprised under the common name of blastula or vesicula blastodermica.
We can, therefore, reduce this cenogenetic form of the discoid segmentation to the palingenetic form of the primitive cleavage.
In both respects the invaluable amphioxus--the sole survivor of the acrania--is found to be the original model that has preserved for us in palingenetic form by a tenacious heredity these most important embryonic processes.
Hence we must once more thoroughly understand the palingenetic embryonic features of the lancelet before we go on to consider the cenogenetic forms of the craniota.
The striking external difference is here again due to the fact that in the palingenetic embryos of the amphioxus (Figures 1.
In this evolutionary appreciation of the facts of embryology we must, of course, take particular care to distinguish sharply and clearly between the primitive, palingenetic (or ancestral) evolutionary processes and those due to cenogenesis.
Its nutritive yelk is much smaller and its formative yelk less obscured with black pigment-cells than in the case of the frog; and its gastrulation has better retained the original palingenetic character.
The segmentation-cells which make up the morula after the close of the palingenetic cleavage seem usually to be quite similar, and to present no differences as to size, form, and composition.
With the formation of the primitive gut our frog-embryo has reached the gastrula stage, though it is clear that this cenogenetic amphibian gastrula is very different from the real palingenetic gastrula we have considered (Figures 1.
This palingenetic fact is the more important, as the greater part of the two body-cavities in Sagitta changes afterwards into sexual glands--the fore or female part into a pair of ovaries, and the hind or male part into a pair of testicles.
I regard all those that diverge from the primary palingenetic gastrulation as secondary, modified, and cenogenetic.
The palingenetic phenomena, or embryonic recapitulations, are due to heredity, to the transmission of characters from one generation to another.
The loftiest and most suggestive of Egyptian palingenetic symbols is unquestionably that of the egg.
The gastrula stage was the palingenetic repetition of the ancestral form of all Metazoa, the Gastræa.
It is worthy of note that the help of comparative anatomy is admittedly required in deciding what processes are palingenetic and what cenogenetic (p.
It supplies a practical criterion for the distinguishing of "heritage" characters from acquired characters, of palingenetic from cenogenetic--a criterion which descriptive morphology was unable to find.
Besides, the special care of the young on the part of the amniotes gives their embryo much more favorable conditions for the cenogenetic abbreviation of the palingenetic evolution.
In the case of these older and lower vertebrates that lived in the water, the embryonic development had the palingenetic character in a still higher degree, as is the case in most of the fishes and amphibia of the present day.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "palingenetic" in a variety of sentences. We hope that you will now be able to make sentences using this word.
