392 SYDNEY J. HIOKSON. 



stock, as they are in the typical phanerocodonic medusa of the 

 Tubularise. 



Comparing the medusa of Millepora with the adelocodonic 

 gonophore (fig. 4) of Hydromedusse, the following points of 

 difference may be observed : 



There is a codonostome in the former, there is none in the 

 latter. 



In the former the endoderm extends almost to the margin 

 of the umbrella, in the latter the endoderm is reduced to a 

 shallow cup surrounding the base of the manubrium. 



In other respects the two gonophores are practically similar. 



Comparing the adelocodonic gonophore (fig. 4) with the male 

 gonophore of AUopora (fig. 5), two points of difference may be 

 observed. In the first place the endoderm completely sur- 

 rounds the gonad in the latter, excepting at a small aperture 

 at the distal pole, where it forms the inner wall of a narrow 

 seminal duct. Secondly, there is no layer of ectoderm between 

 this endoderm and the gonad in Distichopora. In the adelo- 

 codonic gonophore there are two layers of ectoderm between 

 the gonad and the wall of the gonangium. 



The male gonophore of Distichopora (fig. 6) resembles that 

 of AUopora (fig. 5) in all respects except one, namely, that in 

 the former there is no manubrium. 



The female gonophores of the tw^o genera of Stylasteridae 

 resemble the male gonophores in most respects, but in the 

 former there is a more complicated plieting of the base to form 

 a nourishing disc (trophodisc), and no structure corresponding 

 to a manubrium can be observed. 



Do these gonophores of the Hydrocorallinae represent stages 

 in the degeneration, or do they represent stages in the evolu- 

 tion of the free medusiform gonophore ? 



It would be more satisfactory, perhaps, to leave these 

 questions to be answered at a time when we are better acquainted 

 with the minute anatomy of the gonophores of other species 

 of Millepora and the other genera of the Stylasteridse. 



The very convincing proofs that have been brought forward 

 by Balfour, Weismann, and others, showing that the gonophores 



