Notes on some Hydromedusae freni the Bay of Xaples. 579 



I very mucli regret that owing to the quality of material aud 

 its incompleteness I shall not be able to go into any considerable 

 details as to eytolog-ical aspeets of inaturatiou or fertilization, thougli 

 so far as I bave been able to observe there seems to be iiothiug 

 uuiisual iu these respects. 



The germ cells arise in the entoderm of the stem and later 

 segregate within foUicular pouches where they are nourished and 

 complete their growth, the follicles themselves growing aud becomiug 

 eorrespondingly larger, aud more or less hydranth-like, but without 

 trace of teutacles, each however haviug at maturity a protrudiug 

 head, the end of which becomes ruptured for the extrusion of the 

 eggs. Weismaxn has published admirable illiistratious of these 

 features. (Cf. op. cit. PI. 14, Figs. 1 and 2; PI. 15, Figs. 3, 4, 5.) 

 The eggs seem to be discharged singly and fertilization probably 

 occurs duriug this time, follo wing which they become surrounded 

 by a definite tirm membrane within which cleavage aud the deve- 

 lopment of the embryo takes place. Weismann believes that ali 

 the eggs of a given gonophore are discharged at abont the same 

 time and that their cleavage aud siibsequent development proceed 

 simultaneously. In this, however, I am unable to concur. Many 

 cases bave come under my Observation in which considerable Varia- 

 tion in the condition of development of a given Cluster of eggs is 

 «luite evident. This may be readily seen in preparations of entire 

 gouophores, but is strikingly demonstrated from sections of gono- 

 phore Clusters. In Figs. 30 and 31 are shown camera sketches of 

 sections of two eggs of the same Cluster, in the one case the embryo 

 liaving reached the period of definite ectoderma! dififerentiation, 

 while the other is ouly in an early cleavage stage. As compared 

 with other known cases this difference must imply at least a rauge 

 of from fifteen to tweuty hours, and I bave no doubt that others 

 of stili wider divergence are not lacking. Weismann's citation of 

 the notewortby approximation to simultaneous development is, how- 

 ever, well made. It is certainly quite uuusual to tind among hydroids 

 with tìxed sporosacs so near an approach to this coudition as that 

 under consideration. It resembles more the conditious prevaleut in 

 shortlived medusae, like those of Pennaria^ or Pachìjcordyle as 

 described in a preceding section of this paper. The resemblance is 

 the more striking since there is not the remotest approach toward 

 a medusoid character in these simple follicular sporosacs. 



Cleavage begius, as Weismann has shown, very soon after the 



