T. W. Engelmann on the Infusoria. 245 



there existed, besides the two detached halves of the nucleus, a 

 clear, delicate, and sharply defined globular body in the posterior 

 half of each animal. Nevertheless Engelmann did not see this 

 structure in a large number of other specimens at the same stage 

 of conjugation. 



In the course of the further development of the bodies in 

 question, they break up, after attaining their maximum disten- 

 tion, into several (mostly from two to three) spherical segments 

 of nearly equal or of different dimensions. The further history 

 of these corpuscles is unknown, though the idea may be hazarded 

 that they are concerned in the formation of germinal corpuscles. 

 But whether these last, when formed, are further developed into 

 embryos within the parent beings is questionable ; on the other 

 hand, Engelmann traced the re-assumption by a conjugated pair 

 of the ordinary characters of Euplotes Charon without seeing any 

 embryonic development take place. But, further, it is possible 

 that the germinal corpuscles of Euplotes may not, as in Vorti- 

 cellina, attain their maturity within the parent, but may do so 

 externally to it. In this opinion Balbiani seems to concur. 



Engelmann has observed two entirely different forms of con- 

 jugation in Stylonychia pustulata and in S. histrio. In one 

 variety, two originally independent individuals so completely 

 coalesce that in the end the resultant being is undistinguishable 

 from any ordinary example of the species. In the other form, 

 the conjugation is limited in its results to the formation of anew 

 ciliary apparatus on the anterior portions of the conjoined ani- 

 mals, which gradually replaces the old one; after this is accom- 

 plished, separation takes place. This latter form has been 

 already noticed in the case of Euplotes. 



The act of conjugation in Stylonychia pustulata (PI. III. fig. 4) 

 commences by the adhesion of the two animals by their adoral 

 wreaths and strong frontal uncini, so that the left anterior ex- 

 tremity of one is overlapped by the right of the other. Soon a 

 band of union, composed of the substance of the body, unites the 

 two, and gradually increases in width, the bristles and uncini, 

 together with the adoral cilia, disappearing in the meantime in 

 the case of the left individual. Within a short time, the bodies 

 of the two beings have so coalesced that they have an anterior 

 extremity in common, and a divided body posteriorly ; but even 

 this latter indication of their original duality gradually vanishes, 

 until at length the two have become as one being, undistinguish- 

 able from an ordinary species of Stylonychia pustulata, except 

 perhaps that it is commonly broader. In this process the four 

 nuclei have also coalesced into two. This act of complete 

 coalescence is accomplished in from twelve to fourteen hours. 

 On watching the subsequent history of the compound being, it 



