TFi G. VanJS'ame — Embryology of Eustylochus. 265 



of both species the clusters of eggs are usually deposited on the 

 bottom or sides of the jar in which the animals ai-e kept. Some- 

 times they are laid on the surface of the water and float until once 

 submerged, when they sink to the bottom. 



Eggs of Eustylockus ellijyticus. 



The eggs average 0'080™°^ in diameter. Each is enclosed in a 

 tough membrane more than 0-100™™ in diameter, so that the egg 

 is free to move in the clear fluid tilling the intervening space. 

 Owing to the large number of yolk globules which it contains I was 

 able to make out nothing deflnite concerning the internal processes 

 of maturation and cleavage in the entire egg either living or stained. 



Development is very slow and varies greatly in the time occupied 

 in the different stages, so that some of the eggs in a cluster are often 

 farther advanced than. others. In other cases, however, the eggs of 

 the same cluster are in nearly the same stage, 



A few hours after the egg is laid, which occurs more often at 

 night than during the day, it flattens out at one point and the first 

 polar body is given off. The time that elapses before this occurs is 

 probably largely dependent on the tempei'ature, as Francotte found 

 to be the case in the eggs of Leptoplana. The polar body exhibits 

 amoeboid movements both before and for some time after its com- 

 plete separation. Fig. 30 shows the different forms assumed by the 

 polar body in one instance, in the course of ten minutes. When the 

 first polar body has separated the q^^ again becomes sphei'ical but 

 soon flattens again in the same region, and the second polar body 

 separates in a similar manner. Both polar bodies are large, the 

 diameter of the second and smaller one being about one-tenth that 

 of the Q^'^, while the first is about one-half as large again as the 

 second, and usually assumes an elongated form. They usually be- 

 come detached from the ^^^^ after a short time, and float around 

 between it and the egg-membrane, but they show no signs of disin- 

 tegration even after they have been rolled around in this space for 

 many days by the motion of the cilia which develop on the embryo. 

 I have observed no amoeboid movements of the ^^^ itself. 



Some twelve or fifteen hours after the egg is laid the first cleavage 

 takes place, though it may occur sooner or be delayed still longer. It 

 is a vertical and so far as I can determine an equal one. The second 

 cleavage planes are not quite vertical but are so inclined that the 

 somewhat smaller cells that are budded off lie in a slightly higher 



