48 



the difference between this mode of generation and that of 

 the virgin larviparous Aphis is merely in the protrusion of 

 the embryo in the one case through the skin, and in the 

 other through the vagina : both secondary modifications or 

 non-essential accidents of the generative process. In suf- 

 fering to pass uncorrected the term e ovum/ applied figura- 

 tively to these germ-cells of the budding Hydra, in a former 

 Course of Lectures*, published too hastily perhaps, as they 

 were reported by Mr. Cooper, I freely confess that I was 

 justly amenable to the criticism, based on the fact that a 

 true ovum with a bristled chorion had not been shown to 

 exist at the base of the bud. What I believe myself to 

 have stated was, that the true ovum of the Hydra had 

 received the influence of the spermatozoon, and that the 

 primary germ-cell had divided that influence amongst its 

 progeny, which stood in the same relation to the bud as 

 the corresponding derivative germ-cells were afterwards 

 explained to stand to the offspring of the virgin Aphis f. 



No buds are developed from the complex tentacles of the 

 Hydra. Those cells that have been metamorphosed into tis- 

 sues have lost the power of reproducing anything but those 

 tissues or the products of their decay. Had this truth 

 been apprehended by Morren, he would not have imagined 

 that an entozoon could result from the individualization of 

 a previously organized fibre. Many derivative germ-cells 

 and nuclei are retained in the body of the Hydra, each being, 

 in its degree, impregnated ; and this I continue to regard as 

 the condition of its power of gemmation, and also of the 

 fact, that when cut into numerous parts, many Hydrse may 

 be thus artificially propagated. 



The reproduction of parts of higher animals has also 

 been found to depend on pre-existing cells retained as such. 

 Mr. H. D. S. Goodsir has shown that in the Lobster e.g., 

 so noted for the power of reproducing its claws, the rege- 



* 'Lectures on the Invertebrata,' 8vo, 1843, p. 85. 

 t Ibid, pp. 234, 366. 



