166 



OXYCHOPHORA. 



difficulty of obtaining materia], for the eggs, taken from living animals brought 

 to Europe, were sometimes in such a bad condition (Sedgwick, No. 10, Pt. I., 

 Figs. 7-13), that the researches made on them could not be of any great value. 

 Some of the observations also are incomplete, or, as in the case of the South 

 American species examined by v. Kennel, important differences of opinion 

 arise between observers (v. Kennel and Sclater) which can only be finally 

 settled by further research. A connected description of the first ontogenetic 

 processes and their inter-relationships in the various species is as yet impossible. 

 We shall first consider the development of P. novae-zealandiae which, for 

 the reasons given above, we regard as showing the most primitive condition, 

 and then deal with the African species. The South American species, from 

 what we as yet know of them, seem to claim a position distinct from the 

 others. 



Peripatus novae-zealandiae. 



Cleavage is here superficial. The eggs are rich in yolk, and the 



cleavage-nucleus appears to have a peripheral position. Its division 



gives rise to nuclei surrounded by islands of protoplasm ; these for 



the most part also lie peripherally, but single nuclei shift towards 



the centre of the egg, as may be seen in the figures given by Lilian 



Sheldon (Fig. 75, No. 12) 



It is no doubt due to the distribution of the nuclei in the yolk that this latter 

 breaks up to some extent into distinct rounded areas (Fig. 76 A), although 



Lilian Sheldon was not always 

 able to prove that these were 

 regular yolk-pyramids either in 

 origin or form. This break- 

 ing up of the yolk led former 

 observers (Hittton, No. 3, 

 v. Kennel, No. 4, Pt. I.), who 

 could only make observations 

 on insufficient material, to. the 

 conclusion that the egg of 

 P. novae-zealandiae underwent 

 total cleavage. 



According to the descrip- 

 tion given by L. Sheldon, 

 the cleavage - nucleus and 

 the nuclei which first arise 

 seem to lie on the later 

 dorsal side and opposite to 

 the point at which the 

 blastoderm forms. These 

 nuclei increase in number 

 and form a peripheral accumulation (protoplasmic or polar area, Fig. 

 76 A, ft), starting from which, circumcrescence of the yolk takes 

 place (formation of the blastoderm). The active increase in number 



75. — Section through the egg of P. novae- 

 zealandiae (after L. Sheldon). In the yolk are 

 the nuclei surrounded by areas of protoplasm. 



