30 LECTURE II. 



17.), I see a resemblance to the two, four, eight, &c. groups of cells 

 in the mammiferous ovum too striking not to suggest that the 

 process of formation must be the same in both : the essential part of 

 this process consisting in the division of the pellucid nucleus."* Ehren- 

 berg, who, as we have seen, calls this nucleus of the Polygastria 

 the " testicle," views its division simply in the relation of the ne- 

 cessity of each individual resulting from the general fission having 

 such an organ : meaning that each monad, developed by spontaneous 

 fission, is perfected, as regards its so-called testis, by the spon- 

 taneous division of the previous testis, and not by the formation 

 of a new one. But this is not the mode in which the eye, or the 

 circle of teeth, or the pulsating sac, is gained by the second indivi- 

 dual from the fission : the division usually takes place so as to in- 

 clude the original organ in one or in the other moiety ; and that in 

 which it may be wanting gets the organ by a special and independent 

 development of it. The constancy of the preliminary fission of the 

 nucleus would therefore shov/ that it related rather to the totality of 

 the act itself than to the partial completion of the individual in 

 respect of its being provided with a particular male organ of genera- 

 tion. How then, we may inquii'e, does the division of the nucleus 

 relate to the performance of the general act of spontaneous fission ? 

 Our hope of any insight into this mysterious relationship would be 

 from some light to be derived by analogous phienomena. But with 

 what phaenomena is the one in question analogous ? Obviously most 

 closely with those which have been observed in the successive fissions 

 of the impregnated germ- cell of those ova, such e.g. as the ova of 

 the Ascaris (^figs. 48-59.), best adapted to give a view of the fission 

 analogous to those which the perseverance of Ehrenberg enabled him 

 to trace in the spontaneous fission of the monad. 



If this spontaneous fission of the nucleus and germ-cell preliminary 

 to the division of the germ-yelk has not been seen in the ova of other 

 animals, it is because hitherto only the coarser phagnomena of such 

 division of the yelk in the ova of Medusaj, MoUusca, Fishes, Frogs, 

 &c. have been noticed. In Dr. Barry's observations however on the 

 development of the germ-mass in the pellucid ova of the rabbit f, 

 phaenomena were noted closely analogous to those described by Sie- 

 bold and Bagge| in the ovum of the entozoon. 



In reflecting on the cleavage phaenomena in the raonad and the ovum 

 — that a central something is first established, and the consequence 

 thereof — I have been led to draw the same conclusion with respect to 

 both, and to regard the establishment of the special centre as the cause 



* XXVr. p. 24. t XXVII. p. .•i20-.324. % XXVIII. 



