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 Perzpatus, 
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. xove zealandie, 
extremely little in that of P. capenszs. 
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 of 
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 
é form the mouth and the anus. 
In the ova of P. nove zealandie, 
Fic. 169.—Embryos of Perépatws 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 
a., Anus} 82., blastopore; #., mouth; centrolecithal (the type characteristic 
DeSoy Faracive segments; w., zone of of Arthropods), but it is again 
proliferation. true that for a long time the cells do 
not exist as well-defined units. It 
has been said, indeed, that ‘‘the embryo is formed by » process of 
crystallising out 27 széw from a mass of yolk, among which is » proto- 
plasmic reticulum containing nuclei.” 
Zoological positi »n.—The synthetic characters of Pertpatus and 
ils allies may be thus summarised :— 
