154 SOME FURTHER RESEARCHES 



of reproduction (of the Protozoa) is most exactly known in the 

 Gregarince. As a rule, multiplication commences by the con- 

 cresence of two individuals ; this generally occurs very early, so 

 that the two individuals which form one body — the anterior end 

 of one being attached to the posterior end of the other (Fig. 9) — > 

 go on growing for some time ; or conjugation may only take place 

 later when the forms are mature. After this comes a condition of 

 rest, accompanied by encystation, in which the two individuals 

 form a rounded body with a partition between them. Then the 

 partition disappears, and the substance of the body, and also the 

 nucleus, break up into an amorphous mass, from which numerous 

 vesicles gradually arise. From these latter a number of germ cor- 

 puscles, called Pseudo-naviculse (see Fig. 8), on account of their 

 shape, are formed. These gradually fill the whole cyst, and each 

 gives rise to ia single very small organism, consisting of proto- 

 plasm solely, and this being without a nucleus corresponds to a 

 cystoid. Each of these structures moves about in an amseboid 

 manner, and is gradually differentiated into a young Gregarina^ 

 after which a nucleus is differentiated in its interior, and it becomes 

 limited externally by a cortical layer. Although conjugation has 

 no exclusive signification in bringing about these processes, as 

 separate Gregarince are also able to pass through these reproductive 

 processes in just the same way, yet it is not the less important. It 

 points, at least in the cases where it exists, to the necessity of two 

 individuals to bring about reproduction. It is consequently a 

 phenomenon preliminary to sexual differentiation." 



The occurrence of Gregarinae in the Earthworm has been 

 familiar to me, but the cysts do not exhibit the partition so 

 characteristic of these. 



EXPLANATION OF PLATE XVI. 



Ij'ig. 1. — Epithelial and cuticular layers from the integument of 

 Limnodrilus Hoffmeisteri at the period of sexual maturity ; 

 CO,, cuticle ; ee^ epithelial cells ; mm^ circular ; and i^-nlwl 

 longitudinal muscles, 

 j^ 2. —Group of set£e, with young one forming within cell. 



