108 PATTEN. 
The abdominal plate forms an elongated, thick-walled lobe, the posterior half 
of which projects freely from the surface of the egg, a not infrequent abnormality. 
The cephalic lobes are well defined, and in shape and in the numerous small, 
pit-like depressions of the surface suggest the early stages in the cephalic lobes of 
scorpions and spiders. 
The thoracic portion of the marginal fold is very faint except at the anterior 
and posterior ends. 
The posterior margins of the mesodermic area form conspicuous, triangular 
bands, approaching each other toward the median line. Just beneath them in the 
yolk are many degenerating nuclei, especially numerous just beneath the posterior 
median margin, where they form two elongated, parallel cords of yolk nuclei. 
Fic. 15, X 60. This is a remarkably large and well-developed embryo in stage 
D. It represents a type very frequently seen. It is quite normal except in its 
size, in the abbreviation of the abdominal plate, and in the absence of the in- 
vagination of the cephalic lobes. The whole embryo is deeply imbedded in the 
yolk, and with a very prominent marginal fold. There is a series of rounded 
ectodermic thickenings on the outer side of the base of each of the first four 
thoracic appendages, resembling the flabellum of the sixth pair, but being in reality 
the ventral ends of the dorso-ventral muscles. 
