CHAPTER XXI 



MYRIAPODA 



CHILOPODA, THE CENTIPEDES 



Scolopendra cingulata and dalmatica 



The Egg Cleavage and Blastoderm Formation. — The eggs of these two 

 European centipedes are laid during June in the earth at a depth of 3 to 

 8 cm. in clumps of 15 to 20 or more, the female remaining curled around 

 the mass until the young begin feeding. The short ovoid egg averages 

 3 mm. in length and has a thin but brittle chorion. Although the egg 



Fig. 337. — Scolopendra. Median section after intravitelline differentiation of the cleavage 

 cells, (ic) Intercalary cells. {,cc) Cleavage cells. {Adapted from Heymons.) 



contains a protoplasmic reticulum, the meshes of which contain the food 

 yolk, a periplasm is apparently lacking. Shortly after fertilization some 

 cleavage nuclei surrounded by a layer of cytoplasm appear in the yolk. 

 Meanwhile the egg yolk undergoes a pyramidal cleavage (Fig. 337) with 

 the polygonal bases at the egg surface (Fig. 338). A few cleavage cells 

 which Heymons (1901) designates as intercalary cells (i. c) are found on 

 the bounding surfaces of the yolk pyramids, and in the central part of the 

 egg are a number of cleavage cells designated as "pyramid cells" (Fig. 

 337, c. c) . The intercalary cells mitotically divide and migrate toward the 

 periphery, where further cell division takes place, the blastoderm thus 

 arising from isolated cell groups that have developed from the outward 



382 



