ORIGIN OF TFTE SEXUAL CELLS IN HYDROIDS. 621 



Weissmann also describes the process ia Eudendrium 

 ramosuni where the sexual cells are coenosarcal in origin. 



It is important to note that in no case have sexual cells been 

 seen to arise in the hydranth, but always in the trunk of the 

 colony. 



De Varenne has come independently to somewhat similar 

 conclusions, but he goes further and describes a coenosarcal 

 origin where Weissmann had not observed it. 



He shows that in all the forms which he has studied Cam- 

 panularia flexuosa, Plumularia echinulata, Sertu- 

 laria pumila, Gonothyraea Loveni, Podocoryne carnea 

 and Obelia genie ulata, the ova and spermatozoa alike 

 develope in the coenosarc of the trophosorae, and, moreover, 

 originate from endodermal cells, whether they are matured in 

 fixed sporosacs, in medusoids which remain attached (Gono- 

 thyraea Lo veni), or in medusoids which have a free existence ; 

 whether they remain in obvious connection with the eudoderm 

 or migrate so as apparently to lie in the ectoderm. 



De Varenne believes that previous observers who have put 

 forward the ectoderm as the place of origin of the generative 

 products of either sex have been misled by the fact that in 

 many cases, although actually originating as stated above, such 

 cells migrate even after they have reached the gonangium. The 

 endoderm reforms itself beneath the migrated ova or spermato- 

 zoa, a new homogeneous membrane (Stiitzlamella) is secreted 

 by the newly-formed endodermal cells, which might easily be 

 mistaken for the original structureless lamella, the latter as well 

 as the ectodermic layer having become reduced on account of 

 the pressure exercised by the developing egg or spermatozoa 

 to an extremely thin layer, which, however, remains outside 

 the sexual products. 



It has been usual to consider the gonophores, whether these 

 remain fixed (sporosacs) or become free-swimming medusoids, 

 as the sexual persons, the trophosome polyps being asexual 

 persons, but if the observations above recorded are true and 

 should be proved to have the universal application that 

 De Varenne seems to consider they have, the view now usually 



