RELATIONS OF OVA AND GEMM.E. 211 



special conditions, have naturally certain peculiarities in 

 their mode of origin different from those of ordinary buds. 

 Among such peculiarities is their development, in connec- 

 tion with the organs of sex. If there be any truth in the 

 opinion before referred to of the necessary recurrence of the 

 sexual act from time to time in every species, this of all 

 seems the fittest season, when bodies of such importance 

 are to be formed. Such, at least, is the case ; whether the 

 explanation be in point or not, it remains a fact, that the 

 proper gemmae of the gamomorphic stage have always a 

 sexual character. Ordinarily, impregnation is a necessary 

 condition of their ulterior progress ; the transformation by 

 which the gemmae are converted into spermatic and germi- 

 nal elements being apparently incompatible, in most cases, 

 with the farther development of either singly. But in- 

 stances, as we have seen, do occur, in which, either in 

 compensation for the failure of the spermatic element, or 

 for other reasons, the co-related gemma is fitted to retain 

 the power of self-development. Still, however, it acquires 

 somewhat of the sexual character, and may, indeed, in some 

 cases, take on all the structural peculiarities of tlie ovum, 

 and even its capacity, in certain contingencies; for impreg- 

 nation. In every case, there probably remains at least such 

 a speciality of character as clearly to distinguish these 

 gemmae from those developed in any other stage of the 

 genetic cycle.* 



* An exception possibly occurs, in a few species of Polypifera, in the 

 development of the gamomorphic structures themselves (the medusoids) 

 from gemmae having a general resemblance to ova — but the facts of the 

 case are not clear of doubt. See before, in the note at page 129. 



