SUDLER: DEVELOPMENT OF PENILIA. 
Ill 
The second maxilla disappears quite early in the life history of the 
animal, and takes no part in the anatomy of the adult. The six 
pairs of thoracic appendages are all much alike and are all 
biram ose. 
The heart is oval in shape and lies above the intestine just in 
front of the brood-chamber and directly over the shell-gland. It is 
composed of about thirty cells and has one pair of ostia situated 
near the posterior end of the organ. 
The digestive tract has no digestive pouch or gland, but a number 
of gland cells around the pharynx may to some extent take its place 
by secreting similar substances. The intestine curves over against 
the dorsal side of the animal and terminates at the anus between 
two long setae. The shell-glands are nearly round and are com¬ 
posed of from six to twelve large cells surrounding a central lumen. 
This lumen empties to the exterior in the angle formed by the shell 
and the body of the animal. The shape of these glands in Penilia 
is unlike that of any other crustacean. In their histological struc¬ 
ture the cells show an outer striated deeper staining border and an 
inner striated but lighter staining portion. The nuclei stain very 
dark. These cells resemble in structure the secreting cells of the 
homologous glands of Astacus flumatilis figured by Grobben, but 
they are much larger. This comparison must not be carried too far 
as the proportion between the different staining portions is not alike. 
Ordinarily phyllopods show only striated cells, both borders being 
very much alike. 
The ovaries are paired and lie on either side of the digestive 
tract near the posterior end of the animal. They do not exhibit 
the cells arranged in groups of four as Claus describes for Daphnia 
magna or Weismann for Leptodora hyalina , but the eggs are in all 
probability formed in the same manner, i. e. from four cells. The 
absorption and coalescence of the four into one must be quite rapid 
as transition stages are hard to find. 
The brood-chamber lies above and to either side of the digestive 
tract. In cross-section it is heart-shaped with the apex of the 
heart up toward the dorsal side and the depression at the larger 
end of the heart being occupied by the intestine. Its size varies 
greatly, depending upon the number and size of the embryos it may 
contain. 
No males were found among the many hundreds of specimens 
that I have examined. 
