24 DEVELOPMENT OE 



We must, consequently, as far as we at present know, 

 assume that the function of these individuals is fulfilled 

 when the larvae have reached a definite development, that 

 their whole existence has for its object the perfecting of a 

 series of beings of the same species, towards which they 

 stand in the relation of not simply a precedent prepara- 

 tive generation, or brood of feeders, but, inasmuch as they 

 nourish the beings intrusted to them, not by independent 

 and special acts, but hy their life and from their bodies, 

 in that of foster parents {ammende) : and I shall, conse- 

 quently, in what I have to say afterwards, designate them 

 by the short name of Ammen {altrices, " nurses' oy foster- 

 parents.) 



Since, according to the observations of both Sars and 

 Siebold, only animals which have the power of afiixing 

 themselves proceed from the ova of Medusae, all of which 

 become in the way so often described, polypiform 

 " nurses," which nourish the Medusae-larvae from their 

 bodies, a considerable anatomical and physiological 

 difference clearly exists between them, which are all of 

 one sex, and the perfect Medusa which are of two sexes. 

 Here, however, we observe a great natural harmony; 

 since wherever we find the fostering of a brood or fry to 

 be committed to special individuals, these are always of 

 one sex, and indeed females in whom the sexual organs of 

 germination remain in an undeveloped state, whilst in 

 consequence of this abortion in the development of these 

 parts, the instinct or nisus serving for the preservation of 

 the species takes a peculiar direction. 



This representation of their essential sexual relations 

 is not affected by the fact frequently observed by Sars, 

 that the " nursing" individuals increase by gemmation ; 

 in which mode of increase, something more probably can 

 be perceived than the immediate multiplication of the 

 nurses.* 



* Thus it is very remarkable that every part of the body of the "nursing" 

 animals, without mstinction, is capable of tin-owing out gemmae. May not, 

 however, the objection be made, that an ovum might occasionally contain 

 several embryos, one of which has become developed at the expense of the 



