T. W. Engelmann on the Infusoria. 255 



sists in the outgrowth of more or fewer large convex processes 

 from the body of animals found in company with others bearing 

 the embryonic corpuscles. These protuberances are mostly 

 situated on the posterior half of the body, and contain a con- 

 siderable number of small spherical refracting corpuscles, similar, 

 indeed, to others collected in large numbers within the paren- 

 chyma of the parent animalcule. They are evidently the pro- 

 ducts of a fission-process in the nucleus, some very slight rem- 

 nants of which are only now and then perceptible. In one 

 instance these same corpuscles were noticed, though no out- 

 growths existed. The purpose of such products is still a ques- 

 tion. Stein has supposed them to be connected with the origin 

 of the fertilizing elements. 



In Carchesium Aselli Engelmann further observed that pecu- 

 liar condition in which the disk of the peristome assumes a 

 spherical figure and projects from the strongly contracted ani- 

 malcule (PI. III. fig. 13) very much like a yet adherent embryo, 

 but from which it is distinguished by its want of a nucleus and 

 its absence of independent locomotion. If torn from the animal, 

 it does not lose its cilia for some time, though it never swims 

 far with them, but settles down to the bottom of the water, and 

 soon lies motionless there. 



The small corpuscles derived from a breaking-up of the nu- 

 cleus have been seen also in Zoothamnium affine. The processes 

 containing them are of very large size, and either of an elliptic 

 elongated figure or conical and thick, surrounded by a short 

 tubular-looking process, having a distinct aperture at its summit 

 (fig. 14). The corpuscles themselves varied in size, but never 

 exceeded O005 mill. 



The extrusion of embryonic corpuscles was noticed in Vorti- 

 cella Convallaria. Usually, as in Carchesium polypinum, only one 

 such corpuscle, of considerable size, having an opake nucleus, 

 was present. 



The development of germinal corpuscles in Didinium nasutum 

 (Stein) is interesting. This remarkable animalcule ordinarily 

 presents a horseshoe-shaped nucleus, but no nucleolus ; but in 

 October 1860, Engelmann encountered very many specimens in 

 which the nucleus enclosed numerous small spherical corpuscles 

 having a central vesicle in their interior. Among these were 

 several (four to six) considerably larger globular bodies, contain- 

 ing each a distinct nucleus. In other individuals the nucleus 

 was seen divided into several more or less globular segments, 

 lying close together, furnished severally with a nucleus, though 

 still enclosed within the membrane of the parent nucleus. 

 These structures assuredly represent the early phases in the 

 formation of germinal and embryonic bodies. During the trans- 



