19 



state it is liberated from the locomotive germ-mass; but 

 with the exception of a smooth peripheral extensible in- 

 tegument which now invests it, the nuclear matter has 

 exhausted no force in the formation of organs. The nu- 

 clear particles begin first to operate, apparently by self- 

 repulsion, thus making themselves discernible ; and by the 

 attraction and assimilation of the foreign organic matter of 

 the animal which the ciliated parent may have penetrated, 

 a certain growth ensues ; the nuclear contents then resolve 

 themselves into numerous distinct germ-masses. These are 

 in a great degree metamorphosed into the organs of as many 

 Cercariae : the unused- up cells, with the remnant of the 

 spermatic force, are exhausted in converting each Cercaria 

 into an androgynous Entozoon. In this final form the 

 spermatic force is mysteriously renewed in the appropriate 

 male organ ; ova are simultaneously prepared for its re- 

 ception, after which its dissemination recommences by the 

 formation of the germ-mass in each impregnated ovum. 



Here, amongst other topics suggested by the phaeno- 

 mena just described, we may ask, whether all the anima, 

 or manifestations of self-perceptivity and self-activity, of 

 the several e Paramaecioids/ ' king's-yellow worms/ e Cer- 

 cariae' and 'Trematoda/ pre-existed as independent prin- 

 ciples in the single impregnated ovum from which those 

 animals are to proceed. Ajid we might enter upon the inter- 

 esting and important inquiry how, and how far, these phae- 

 nomena of Parthenogenesis may determine the long-mooted 

 question of the relation of such vital principles or manifes- 

 tations to the organization of the individual. But this is 

 foreign to my present object, if even time permitted, and 

 I proceed therefore to the other instances of cyclical ge- 

 neration. 



V. Baer, who led the way in experimenting and ob- 

 serving the artificially impregnated eggs of the Sea-urchin 

 (Echinus), found them to be first developed into a ciliated 

 monadiform animalcule, like that of the Medusa aurita. 



