Developmental History of Infusorial, Animal Life. 371 



perfect animal. In this form of reproduction animals are 

 formed, not from ova,, or from the fission of primary repro- 

 ductive cells, but from secondary or derivative germ-cells, 

 placed in reserve in the tissues of these animals. The same 

 process occurs in the Triton or the lobster, when a broken-off 

 claw or tail is replaced, the new formation springs from deri- 

 vative germ-cells placed in the claw or tail — that is, a reserve 

 of derivative germ- cells, not wanted for use in the general 

 development, is deposited in these different parts of the body."* 



Professor Goodsir believes that " the regenerative faculty 

 does not reside at any part of the claw of the lobster in- 

 differently, but in a special locality at the basal end of the 

 first joint. This joint is almost filled by a mass of nucleated 

 cells surrounded by a fibrous and muscular band."" 



With respect to the Hydra, its reproduction is indifferently 

 by gemmation or by true ova. The young hydra from the 

 egg is identical in structure and character with that produced 

 by budding. Nearly all writers now regard gemmation and 

 generation by ova as two essentially distinct processes ; never- 

 theless, the identity of the results is clearly seen in Mr. R. 

 Crouch's observations on the Sertulariau Polyps. " At certain 

 seasons of the year," he says, "they produce cells much 

 larger than those of a more permanent character. These are 

 at first composed of the granular pulp of the stem, afterwards 

 the pulp becomes furrowed, and finally formed into cells. 

 After a short period they separate from the parent, and undergo 

 the process of development. If these cells attain a certain 

 size they are developed into eggs : if, on the other hand, they 

 are stunted by cold, or otherwise interfered with, they are 

 formed into polyps, while, if from further unfavourable circum- 

 stances they are rendered still smaller, they grow into branches, 

 and thus we see that, according to circumstances, different 

 organs are capable of being eliminated from the same 

 structure." 



It appears, then, that there are three forms of reproduction, 

 fission, gemmation, and generation by ova ; in other words, 

 " Fissiparous, when a cell spontaneously divides into two or 

 more : Gemmiparous, when a plant or animal sends forth young 

 branches from its stem ; Oviparous, when the young are pro- 

 duced from seeds or eggs." If we endeavour to arrange the 

 known facts of reproduction, proceeding from the simple to 

 the more complex, we must begin with a very simple process ; 

 namely, that of a single cell spontaneously multiplying itself 

 by subdivision. In all the albuminous, starchy, or gelatinous 

 matter called protoplasm* a single cell appears, it assimilates : 



* Huxley's Lectures on Comparative Anatomy. 



t Protos (ivpSiios) lirst, plasma (irAc&tr/xa) formative substance. ■ .'•.'•■ 



