92 ORGANIZATION OF THE INFUSORIA. 



that corresponds most closely with this important function as it is met 

 with in all Metazoic or multicellular structures. As already maintained 

 in the description of that more common phase of multiplication which 

 takes the form of constantly repeated binary division, the Infusoria 

 through such mode of increase merely repeat in a separate and inde- 

 pendent manner that process of cell-multiplication which characterises the 

 normal growths of all tissue structures. By-and-by, however, in the case of 

 the Metazoon or tissue organism, an epoch is arrived at when the com- 

 ponent cells cease to exhibit their previous duplicative energy, the conse- 

 quence being the gradual decay and ultimate dissolution or death of the 

 entire organism. But for the interposition of a special and more or less 

 periodical regenerative act, this termination of the life of the individual 

 would also, sooner or later, involve the extinction of the race or species. 

 Such a regenerative act, and the further survival of the race, is, however, 

 here accomplished through the fusion or union of one of that congeries of cells 

 out of which the compound organism is composed with one other exteriorly 

 derived cell liberated from another organism or congeries of cells pertaining 

 to the same specific type. The result of such fusion between these two, 

 denominated respectively the germ-cell and sperm-cell, or, in other words, 

 the ovum and spermatic cell or element, is the capacity conferred upon the 

 former of once more proceeding with the duplicative process, and repeating 

 that cycle of cell-aggregation or tissue-construction followed by the parent 

 organism. In a precisely similar manner, the infusorial body, after repeated 

 duplicative multiplication, arrives at a condition in which the strain or 

 race is too exhausted for the further maintenance of this process, and 

 without the intervention of some supplementary regenerative operation 

 would become extinct. By, however, the coalescence or fusion of one of 

 these individual cells or animalcules with an elemental cell or animalcule 

 derived from a neighbouring race or strain, the capacity to continue the 

 duplicative process is revived, and the further duration of the race secured. 

 The two animalcules thus uniting with one another correspond to all intents 

 and purposes with the coalescing germ-cell and sperm-cell, or ovum and 

 spermatozoon of the higher tissue organisms, the only essential point of 

 divergence being in the subsequent changes manifested ; the organism in 

 the latter instance exhibits a tendency to build out of the cells amassed 

 by the duplicative process, more or less complex coherent tissues, while in 

 the former each cell so produced maintains a separate and independent 

 existence. 



Among the extensive series of types included in the infusorial classes, the 

 phenomenon of " conjugation," " fusion," or " zygosis," as it is variously called, 

 and which undoubtedly represents the sexual or genetic reproductive process 

 of the higher animals in its most simplified or elementary form of expression, 

 exhibits certain well-defined modifications. With the majority of the more 

 highly organized Ciliata, such conjugation has to be denominated, as com- 

 pared with the form next described, transient and incomplete, being, as 



