1908.] GROON-ES IX A MEDUSA. 57 



an obvious and natural channel for their transit to the exterior. 

 The groove is not closed dorsally, it is true, but the epithelial 

 ridges bounding the groove seem capable of approximating 

 sufficiently closely that it is by no means difficult to imagine the 

 groove as practically a closed canal — a functional gonoduct, in 

 short. 



It must be admitted that I have not been able to detect the 

 presence of sex-cells in the gonadial grooves, but this may be due to 

 the fact that the gonads were not mature, or the sex- cells ripe for 

 extrusion. It remains for further investigation to ascertain on. 

 living specimens under suitable conditions whether these views as 

 to the nature and function of the gonadial grooves are correct. 



A careful examination of Pelagia noctiluca and CJirysaora 

 isosceles, both of which belong to the Pelagidae, failed to reveal the 

 existence in either species of any structures comparable to the 

 gonadial grooves of Aurelia aurita. 



In conclusion, it may be suggested that the observations 

 recorded above possess certain features of more general interest. 



In discussing the evolution of the ccelom Sir Ray Lankester* 

 remarks : — " We may suppose the first ccelom to have originated 

 by the closing or shutting off of that portion of the general 

 archenteron of Enteroccela in which the gonads develop, as in 

 Aurelia or as in Ctenophora " ; and, further, " the most important 

 developments of the ccelom are in connection -v^-ith the establish- 

 ment of an exit for the generative products through the body- 

 wall to the outer world." If, therefore, my observations and 

 inferences as to the nature and function of the gonadial grooves 

 be correct, it is obvious that in this organism we have an 

 extremely interesting and primitive condition. 



The gastric pouches are special portions of the archenteron, 

 from the walls of which the gonads have their origin ; they are, 

 in fact, primitive gonocceles, although not yet completely shut off 

 from the general archenteric cavity as is the case in so many 

 Ccelomata. On the other hand, the gonadial grooves may be 

 regarded in the light of incipient cicelomoducts or gonoducts 

 which in like manner are still but imperfectly constricted off from 

 the archenteron. Consec^uently the gonadial grooves and gastric 

 pouches of Aurelia seem to represent a very primitive stage in 

 the evolution of both gonocceles and gonoducts. 



It has generally been held that, with one exception, the 

 Coelenterata have no specially differentiated genital ducts, the 

 sex-cells finding their way to the exterior either directly by the 

 external dehiscence of the gonads, or indirectly by internal 

 dehiscence into archenteric canals or spaces and thence outwards 

 through the mouth. The single exception referred to is in the 

 case of Cteaoplaaa korotnefii, the aberrant Ctenophor discovered 

 by Willey t in 1896 in the Eastern Archipelago of British Xew 

 Guinea, in which, however, only male gonads were found. 



* A Treatise on Zoology, part ii. 1900; p. 9. 



t Quart. Journ. Micros. Science, vol. 39, u. s, 189&-97. 



