DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 183 
We may therefore look upon the ovum of the Cape Peri- 
patus as presenting two different modes of segmentation, 
neither of which are instances of complete cleavage in the 
ordinary acceptation of the term. 
First, there is the segmentation preceded and apparently 
determined by the division of the nucleus of the fertilised 
ovum and its products. This process gives rise to the ecto- 
derm cells. 
Secondly, there is the division of the larger and clearer 
vegetative part of the ovum into the endoderm masses. This 
process takes place contemporaneously with the first, but 
apparently without being governed by the dividing nucleus of 
the animal or ectodermic part. At any rate no part of the 
latter enters the endoderm masses. It is true that the endo- 
derm masses in the fresh state do present a central opaque 
portion (Part 1, fig. 8,) but I was unable by any of the staining 
methods I adopted (borax-carmine, hematoxylin) to find any 
trace of a structure like an ordinary nucleus in preserved 
specimens of the segmenting stages, though nuclei were easily 
visible in the endoderm of the gastrula and later stages. I 
did find, however, in my stained section of preserved seg- 
menting ova, that the endoderm masses presented a central 
portion in which the spongework was much denser than in the 
peripheral parts (Pl. XIII, figs. 16, 17). But this central 
denser portion was entirely without the especially deeply-stain- 
ing chromatin so characteristic of the ordinary nucleus. This 
is especially shown by fig. 16. On the other hand, there are 
in the strands of the network of the endoderm masses small 
particles of a deeply-staining matter, which are neither visible in 
the unsegmented ovum nor in the gastrula stages, and which are 
not to be distinguished from nuclear chromatin. These deeply 
staining bodies are found in great numbers in the endoderm 
masses (fig. 16), and to avery small extent in the ectoderm 
cells. Have these central dense portions of the endoderm 
masses and the scattered deeply-staining bodies any hand in 
giving rise to the undoubted nuclei which subsequently appear ? 
In other words, are these structures to be looked upon as 
