ON NAUTILUS AND SOME OTHER ORGANISMS. Sd 
were arranged spirally, the spirals being here and there in- 
terrupted (Fig. 7). The egg-disc measured 15 mm. in diameter. 
Fic. 7.—Enlarged view of the egg-dise of Planocera discus. Only a 
few of the egg-capsules have been inserted in the drawing. 
Each row consists of numerous capsules packed closely to- 
gether in what amounts to a common gelatinous tube. The 
spirals can be unwound. In the outermost spiral were a few 
irregularly dispersed capsules. The normal capsules contained 
each from eight to eleven ova, and the latter had no other 
membrane round them individually. 
On May 4th the same individual, which had been kept 
isolated all the time, laid another much smaller disc of egg- 
capsules. I left these undisturbed, and in the course of time 
many of the ova developed into ciliated embryos with a pair of 
large primary eyes. The embryos swim about actively in the 
capsules, three or four to seven or eight in each capsule, sur- 
rounded by the fragments of those eggs which had not de- 
veloped. Many of the embryos had developed abnormally, 
owing probably to the fact that the water in which they were 
kept had not been changed frequently enough. Before seg- 
mentation commences, some of the ova in each capsule present 
