GENETIC REPRODUCTION. 93 



illustrated by the generic type Paramecium, accompanied by the following 

 manifestations. Two previously independent and free-swimming zooids 

 meeting one another, become locked together through the close applica- 

 tion and apparently intimate union or coalescence of their two oral or ventral 

 surfaces, the aspect presented by the united couple coinciding closely with 

 that of longitudinal fission as it occurs among many familiar types, and for 

 which simple reproductive process it was originally mistaken by Ehrenberg 

 and other early writers. This process of conjugation or fusion has in the 

 present species been observed to extend over a period of five or six days, 

 the two united animalcules swimming about in the interim with an amount 

 of ease and activity scarcely inferior to that exhibited by the single and 

 independent zooids. The genera Bursaria, Blepharisma, Chilodon, Cyrto- 

 stomum, and many other forms, exhibit conjugative .phenomena closely 

 identical with those presented by Paramecium, while in Stylonychia it would 

 appear, according to Engelmann, that both the transient and the complete 

 form of conjugation may be met with among individuals of the same species. 

 In the normally stationary or attached genus Stentor the conjugative process 

 is also transient, the contiguous animalcules, according to Balbiani, becoming 

 temporarily united by their anteriorly located oral areas. A similar tran- 

 sient conjugative act has likewise been reported to obtain among the 

 members of the genus Podophrya, but, as shown by the author in the case 

 of P. mollis, such apparent act is not unfrequently attributable to the less 

 complex process of multiplication by binary division. 



The form of conjugation to be next enumerated is characterized by 

 its complete and permanent duration. Two animalcules or zooids in this 

 case become, as it were, so completely melted or welded together, that 

 their previous individuality is entirely obliterated. Among the Ciliate 

 section of the Infusoria, this special complete or entire conjugative phase 

 is almost exclusively restricted to the Peritrichous family of the Vorticellidae, 

 but recurs occasionally in alternation with the partial or transient one in 

 Stylonychia and other Hypotricha. The most prominent development of 

 this permanent or complete type is undoubtedly met with in the Flagellate 

 section of the series throughout the whole of which, as at present known, 

 it would appear to constitute the one and only conjugative process. 

 Most usually, among these Flagellata, this complete conjugative act 

 is accompanied with the assumption by the coalescing individuals of 

 an outline entirely at variance with the normal specific aspect. The 

 flagella or other appendages are in this instance entirely withdrawn, 

 and pseudopodic processes, like those of an Amoeba or Actinophrys, 

 extended for locomotive or prehensile purposes from various parts of the 

 periphery. Succeeding such conjugation among the Flagellata, it most 

 usually happens that the sporular reproductive phase, described on a pre- 

 ceding page, is immediately entered on, though that such conjugation is 

 not imperatively associated with this spore-production has been demon- 

 strated by the present author, in connection with Heteromita angustata, and 



