MYRIAPODA 



383 



migrating intercalary cells. At one point on the ventral egg surface cell 

 division is more active, giving rise to a small nearly circular germ disk. 

 This is in evidence even before the formation of the blastoderm in S. 

 dalmatica, but in S. cingulata the blastoderm forms first, the isolated cell 

 groups eventually becoming contiguous by single cells wandering into the 

 intervening spaces. 



if-emb 



Fig. 338. — Scolopendra cingulata. (emb) Embryonic rudiment, (cp) Cumulus primitivus 

 (early rudiment), {yp) Yolk pyramid (macromere). (Adapted from Hey mons.) 



Germ Layers. — The germ disk by rapid mitotic division soon becomes 

 several layers thick (Fig. 339), in structure resembling the cumulus 

 primitivus in spiders, the yolk masses immediately below being broken 

 up. A few cells set free from the inner surface wander into the yolk, 

 forming yolk cells, which are found not only on the dividing surfaces of 



Fig. 339. — Scolopendra cingulata. Section through early rudiment, (blast) Blastoderm. 

 (cp) Cumulus primitivus (early rudiment) . (ent) Entoderm cell. (Adapted from Heymons.) 



the yolk pyramids but also in the peripheral part of the pyramids. A few 

 degenerating cells, the paracytes, may also be observed. Later yolk cells 

 are also gradually given off from the inner surface of the blastoderm. 



The formation of the entoderm takes place in the same manner as that 

 of the yolk cells. Cells are set free frorh numerous points of the inner 



