THE MALAYAN SPECIES OF ONYOHOPHOEA. 43 



the small clear spaces or alveoli of the cytoplasmic network 

 of the previous stages become darker than the intervening 

 substance, a result probably brought about by the deposition 

 in them of fine granules of food-yolk (PI. 8, fig. 18 c). As 

 the ovum increases in size the granules seem to run together, 

 and consequently to form larger bodies, which in mauy cases 

 appear to fuse so as to form structures which may be de- 

 scribed as systems of granules Avhich present several centres 

 of deposition, as well as a common surrounding coat (PI. 8, 

 fig. 18 d). 



The nucleus, at the commencement of the period of growth, 

 is situated at or near the centre of the cell, and presents a 

 regular oval outline ; but towards the end of the period in 

 question it moves nearer the surface. While this transference 

 is being effected it presents an irregular outline, and seems 

 to influence the general arrangement of the yolk bodies 

 situated in its immediate vicinity (PI. 8, fig 18 d). 



The fully grown ovum possesses a fairly thick coat, pre- 

 sumably a vitelline membrane, and is furthermore surrounded 

 by a layer of cells derived from the wall of the ovaiy : it is 

 suspended, by means of a cord of cells, in the body-cavity. 

 Dr. Willey used the term " exogenous" to describe this method 

 of origin, in contrast to that found in the genus Peripatus 

 in which the ova are formed " endogenously " (7). 



The fully grown or mature ovum is oval in shape, provided 

 it has sufficient space to assume its proper form; otherwise, 

 under pressure exerted upon it by the neighbouring organs, 

 it may become quite irregular in outline. 



The difference existing betweeu the modes of origin and 

 structure of the ovum in the closely related genera Peri- 

 patus and Eoperipatus is worthy of note, and is probably 

 the main cause of their divergence in development. 



III. A General Account op the Development viewed 



EXTERNALLY. 



In each uterus of Eoperipatus weldoni there may be as 

 many as a dozen embryos, ranging in development from 



