DEVELOPMENT OF THE CAPE SPECIES OP PEIUPATUS. 517 



caution in dealing with the general importance of the phe- 

 nomenon. 



I shall assume, then, to start with, that the ovum of the 

 Cape species has only recently lost it yolk, and that it may 

 be compared to an ovum of the New Zealand form from which 

 the yolk has been almost completely dissolved out by some 

 reagent. As a matter of fact, it is impossible, with our 

 present methods, to effect this complete solution of yolk and 

 leave its protoplasmic framework ; but what we cannot effect 

 has been done by nature in the most complete manner, leaving 

 an ovum which is little more than a loose protoplasmic sponge- 

 work, excepting at one point where the protoplasm is more 

 dense. It is at this point only that the cleavage takes place; 

 for the breaking up of the rest of the ovum into irregular 

 masses cannot be regarded as a process^ in any way related to 

 cleavage, inasmuch as the nucleus takes no part in it. 



The cleavage would appear, therefore, to be meroblastic, and, 

 as in meroblastic ova, the protoplasm round the nuclei at the 

 periphery of the blastoderm is perfectly continuous with that 

 of the main mass of the ovum in which the yolk is contained, 

 but from which it is absent in this ovum ; that is to say, we 

 have round the periphery of the blastoderm, and lying in the 

 part of it which corresponds to the yolk of large-yolked mero- 

 blastic eggs, a number of yolk-nuclei, or rather of nuclei 

 which correspond to the yolk-nuclei of such large-yolked eggs. 



But the cleavage is not only meroblastic, it takes place in 

 the same manner as in centrolecithal ova, i. e. the furrows 

 extend only a short distance into the ovum {vide Part II of 

 this series, p. 179) ; the deeper parts of the segments are con- 

 tinuous with each other. Very soon, however, the loosely 

 reticulated protoplasm extends on to the contiguous surfaces 

 of the segments, from which it was at first absent owing to the 

 fact that the furrows are formed in the densely reticulated pro- 

 toplasm only. It thus happens that each segment becomes 

 continuous with all the contiguous segments near the surface, 



' This process is probably identical with the formatiou of the non-nucleate 

 yolk-spheres found in many Arthropoda. 



