34 THE ANATOMY AND DEVELOPMENT OF PERIPATUS NOVAE-BRITANNTAE. 



P. capensis the egg, as shown by Sedgwick, is large and contains vesicular protoplasm. 

 Sedgwick very naturally supposed that this indicated a loss of yolk which had formerly 

 filled the vacuoles at present occurring in the egg — especially in view of the yolky egg 

 of P. novae-zealandiae. The view that the egg of Peripatus capensis exhibits a stage 

 in the process of acquiring yolk instead of being a stage in the loss of yolk, could 

 be sustained with equal force. There is no means at present known of deciding 

 between these two views in this particular case. Both of them seem to be equally 

 possible. In the egg of P. novae-britanniae however, as well as in those of the 

 Neotropical species of Peripatus, this difficulty is not present, since there is no reason 

 whatever to suppose that there has been a secondary loss of yolk in these cases. 



Yolk may be defined as reserve nutrient matter derived from the maternal organism 

 and deposited in the egg in a sub-solid form. Fat is an analogous reserve food-stuff 

 stored up by various animals for use in times of low-feeding or of cessation of feeding, 

 and derived from foreign ingested nutrient matter. 



As has been described above, in the late embryos of P. novae-britanniae at a time 

 when they are approaching the period of birth, large and small globules of reserve 

 nutrient matter — the eosinophile globules — make their appearance in the endoderm. 



Whatever the chemical constitution of these globules may be, whether allied to 

 fat or to lecithin, the fact remains that they are yolk-like globules deposited in the 

 endoderm of the late embryos and derived, like true yolk, from the maternal organism. 

 It thus appears possible that the early appearance of yolk in eggs which contain yolk 

 is only a special case of the nutrition of the embryo at the expense of the maternal 

 organism, and that reserve nutrient matter of a like nature, so far as function (i.e. 

 nutrition of foetus) is concerned, may appear at a much later stage in the development. 



The fact of these eosinophile globules making their appearance in the endoderm 

 is of interest since the seat of yolk in eggs is essentially at the vegetative pole 

 which later gives rise to the endoderm. 



Thus it will be seen that within the limits of the genus Peripatus we are con- 

 fronted with a problem with regard to the lecithality of the ovum, which is exactly 

 analogous to that presented by the Mammalian ovum. I suppose many embryologists 

 take it for granted that the yolkless condition of the ova of the higher Mammals is 

 quite a secondary condition. It is therefore interesting to note that one of those best 

 fitted to judge does not hold this opinion. I refer to Professor Hubrecht. 



As for Peripatus all I can say, with the limited experience which I have had 

 of this remarkable genus, is that it appears to me to substantiate the principle upon 

 which Prof. Hubrecht's views are based. 



PHYLOGENETIC CONSIDERATIONS. 



The fundamental differences in the early development of the four known subgeneric 

 groups of Peripatus which at first appear to be so unaccountable, may, by their very 

 diversity, afford a clue to the phylogeny of Peripatus. 



This subject has been already speculated upon by Kennel. 



With the knowledge available at the time Kennel wrote, he said that it seemed 

 certain that within the limits of the genus Peripatus the method of embryonic develop- 



