SUDLER : DEVELOPMENT OF PENILIA. 
125 
of the ventral nerve cord reveals a section shaped somewhat like a 
dumb-bell, showing that while the ganglia unite they do not entirely 
lose their double character. 
The Eye. 
The eye of the adult Penilia is quite small in comparison to that 
of other Cladocera. Its development and separation from the 
brain rudiment do not take place until quite late. The rudiments 
of the eye of Penilia do not arise separately or around distinct 
centers, but they are plainly seen to be lobed and paired to that 
extent. 
The Digestive Tract. 
The beginning of the mid-gut of Penilia is seen when the inwan- 
o o o 
dering of cells occurs at gastrulation. The rod of tissue thus formed 
breaks away or very nearly so from the ectoderm, but retains its 
general position in the long axis of the embryo. The rod is solid, 
but is not regular in outline or cylindrical at first. See Figs. 15, 
16, 17, 30, 31, and 32. Later this indefinite rod assumes definite¬ 
ness, and at a stage shown in Fig. 26 the mid-gut shows as a clearly 
defined cylindrical rod arranged radially. Later when the embryo 
enlarges and begins to assume the adult form, as at a stage repre¬ 
sented by Fig. 28, the lumen appears. The mouth and pharynx 
are formed from an inpitting which Occurs just under the rapidly 
elongating upper lip. The origin of the anus is also from an inpit- 
ting of the ectoderm at the opposite end of the embryo. Whether 
this inpitting occurs at the same spot at which gastrulation occurred 
or whether it is entirely new, I am unable to state definitely, but, 
judging from the position of the gastrula mouth when the embryo 
is revolved, I think the anus is formed dorsal to it. The anus 
forms in Penilia directly in the center of the posterior end and in 
the mid-line, while the position of the gastrula mouth when the 
embryo is revolved is in the mid-line but considerably ventral to 
the center of the posterior end. Grobben finds the anus of Moina 
arising at the posterior dorsal angle of the embryo. He also finds 
that the mouth and anus appear earlier in Moina than in Penilia. 
According to Samassa we do not have an entodermal rod as dis- 
