GREGA1UNIDA. 29 



viscid fluid holding in suspension rounded granules, among 

 which the nucleus rests. This nucleus contains an inner 

 vesicle or nucleolus, which strangely disappears and then 

 reappears. Van Beneden distinguishes three kinds of mo- 

 tions in the Gregarinaj : 1. They represent a very slow 

 movement of translation, in a straight line, and without the 

 possibility of distinguishing any contraction of the walls of 

 the body which could be considered as the cause of the 

 movement. It seems impossible to account for this kind of 

 motion. 2. The next kind of movement consists in the 

 lateral displacement of every part, taking place suddenly 

 and often very violently, from a more or less considerable 

 part of its body. Then the posterior part of the body may 

 be often seen to throw itself out laterally by a brusque and 

 instantaneous movement, forming an angle with the anterior 

 part. 3. Owing to the contractions of the body, the gran- 

 ules within the body move about. 



The life-history of this Gregarina is as follows : It occurs 

 in its normal state in lobsters in May, June, and August, but 

 in September becomes encysted in the walls of the rectum of its 

 host, the cysts (Fig. 18, A] appearing like little white grains 

 of the size of the head of a small pin. When thus encysted 

 the nucleus disappears, and the granular contents of the 

 cyst divide into two masses (B], like the beginning of the 

 segmentation of the yolk of the higher animals. The next 

 step is not figured by Van Beneden, and we therefore intro- 

 duce some figures from Lieberkuhn which show how the 

 granular mass breaks up into spindle-shaped bodies (called 

 by some authors " pseudonavicellae," and by Lieberkuhn 

 " psorosperms") with hard shells. After the disappearance 

 of the nucleus and vesicle, and when the encysted portion 

 has become a homogeneous granular mass, this mass divides 

 into a number of rounded balls (Fig. 18, C). These balls 

 consist of fine granules, which are the spindle-shaped bodies 

 in their first stage (Fig. 18, N). They then become 

 spindle-shaped (0] and fill the cyst (Fig. 18, M), the balls 

 having meanwhile disappeared. From these psorosperms 

 are expelled amoeba-like masses of albumen (D E ), which, 

 as Van Beneden remarks, exactly resemble the Frotaniceba 



