112 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The Development of the Eggs. 
The eggs of Penilia when laid are oval and much longer than 
broad, measuring from 100 or 110 fx in length and 20 or 30 /x in 
breadth. Usually from four to six are deposited at one time, 
although the number may range from one in young or small ani¬ 
mals to eight in large well-developed adults. Generally the same 
number is laid on either side but exceptions to this are found. 
According to Grobben the brood-chamber of Moina rectirostris 
may contain twenty-two eggs, and he has seen as many as thirty 
well-developed embryos in that of Moina paradoxa. 
The egg of Penilia contains but little yolk and possesses a small 
deep staining nucleus surrounded by a circle of clearer protoplasm. 
They have a vitelline membrane and never at any stage do they 
possess more than the one. Lebedinsky found two in Daphnia 
similis , a chorion and vitelline membrane. Grobben always found 
but the one (vitelline) in Moina. I think the egg of Penilia repre¬ 
sents the surviving cell of four homologous cells, and for these 
reasons. The ovary is usually seen to be made up of cells arranged 
in quite a definite manner. At the posterior end the cells are of 
different sizes and arranged in no regular order. This is the ger¬ 
minal epithelium. At the anterior part a row of cells alike in size 
and appearance occurs. These, however, are not arranged in sets 
of four so as to give the whole a bead-like structure, as is seen in 
Daphnia and Leptodora, but they are always some multiple of four. 
As the usual number of eggs found on a side is three, so the usual 
number of cells seen in ripening ovaries is found to be twelve. The 
smallest number of these cells when any at all are present is four. 
The size of these four cells is slightly larger than that of the mature 
egg; but the size of the egg corresponds very nearly to the size of' 
them all, and is therefore very much larger than any one cell. In a 
few (three) specimens I have seen what I have taken to be the act 
of fusion. Nuclei in partially broken states occurred in protoplasm 
which seemed separated in places and slightly broken and irregular. 
This fusion of the four cells must occur quite rapidly as transition 
stages are so rare. In some cases, in eggs which had not seg¬ 
mented, small fragments of material which stained as nuclear 
material appeared. These were embedded in the substance of the 
egg, and I interpreted them as fragments of the nuclei of the three 
cells that lose their identity in the formation of the egg. I found 
