322 



PHYLUM ARTHROPODA. 



of the anus. In the ejaculatory duct the spermatozoa, which are 

 thread-like, are made into spermatophores which are attached to 

 the female. It is uncertain how the spermatozoa get into the female. 

 Fertilisation is ovarian. 



While it is characteristic of Arthropods, in which chitin is so pre- 

 dominant, that ciliated epithelium is absent, it seems that in Pertpatus, 

 which is much less chitinous than the others, ciliated cells occur in 

 some parts of the reproductive ducts. 



Development. There is some variety of development in different 

 species. Thus there is much yolk in the ovum of P. nov<z zealandia, 

 extremely little in that of P. capensis. 



In P. capensis the "segmentation" 

 is remarkable, for true cleavage of 

 cells does not occur. The fully 

 " segmented " ovum does not exhibit 

 the usual cell limits. It is a proto- 

 plastic mass or syncytium with 

 many nuclei. Even when the body 

 is formed, the continuity of cells 

 persists, nor does the adult lack 

 traces of it. To Prof. Sedgwick this 

 singular fact suggested the theory 

 that the Metazoa may have begun 

 as multinucleate Infusorian-like ani- 

 mals. 



The gut appears from a fusion ol 

 vacuoles within the multinucleated 

 mass, and a gastrula stage is thus 

 established. A very interesting 

 feature is that the blastopore or 

 mouth of the gastrula is first elon- 

 gated, then dumb-bell shaped, then 

 closed except at the two ends which 

 form the mouth and the anus. 



In the ova of P. nova zealandicz, 

 FIG. 169. Embryos of Peripatus which have much yolk, a superficial 

 capensis, showing closure of multiplication of nuclei forms a sort 

 blastopore and curvature of of blastoderm, which spreads over 

 embryo. After Korschelt and almost the entire ovum. The seg- 

 Heider. mentation in this case has been called 



., Anus ; /., blastopore; m., mouth ; centrolecithal (the type characteristic 

 p.s., < primitive segments; ;., zone of of Arthropods), but it is again 

 proliferation. tme tnat f or a j ong t i me tne cellg ^ o 



not exist as well-defined units. It 



has been said, indeed, that " the embryo is formed by a process of 

 crystallising out in situ from a mass of yolk, among which is a proto- 

 plasmic reticulum containing nuclei." 



Zoological position. The synthetic characters of Peripatus and 

 its allies may be thus summarised : 



