THE CALYCOPHORIDiE. 27 



gularly developed ; but it is only in the CalycophoruJa, in the Velellida} and in some 

 CorynidcB and Sertulariada-, that the development of the medusiforra generative zooids is to 

 be observed in full perfection. 



The first stages in the development of these bodies precisely resemble those exhibited 

 by the ordinary nectocalyces ; but when the longitudinal canals are making their appearance, 

 the central boss does not remain convex at its apex. On the contrary, it becomes excavated 

 at this point, and the excavation gradually extending distally, eventually takes the form of a 

 saccular diverticulum of the cavity of the organ, occupying the axis of the boss, and extending 

 for a greater or less distance tovi^ards the distal end of the organ. It, therefore, lies in the 

 middle, between the four longitudinal canals, and nearly takes the place of, though it by no 

 means represents, the central cavity of the nectocalyx. The latter is, in fact, in consequence 

 of the appropriation of the greater part of the substance of the boss to form the walls of this 

 central cavity, reduced to a mere fissure, which gradually separates that part of the organ 

 which contains the system of canals (as the calyx) from a free central sac (the manubrium), 

 connected with the calyx only opposite the peduncle. An opening is formed at the distal end 

 of the calyx, and becomes surrounded by a valvular membrane in the same way as has been 

 described above for the nectocalyx : finally, as the fissure widens, that wall of it which 

 belongs to the calyx becomes more and more widely separated from the central sac, and 

 acquires a muscular structure. 



The calyx is thus exactly comparable to a bell, and the manubrial sac to its clapper, 

 while the peduncle is its handle. The future fate of the body thus formed varies. In some 

 cases it remains attached by its peduncle, and the ova or spermatozoa making their appear- 

 ance at a very early period in the walls of the sac, which never opens at its apex, are 

 detached, apparently by the dehiscence of its outer wall; or the manubrium, having the 

 same structure and being nothing but a genital sac, does not get rid of its products until the 

 whole body has been detached from its peduncle, and swims about independently ; or the 

 reproductive elements may not have appeared in the walls of the manubrium when the organ 

 is detached, and then the sac opens at its end and becomes functionally and structurally a 

 polypite. The reproductive elements are ultimately developed either in its walls or in those 

 of its system of canals ; or it may be that such bodies are in some cases ( Willsia, Lizzia ?) 

 mere gonoblastidia, whence the true reproductive apparatus is eventually developed. 



' Sars (' Fauna,' p. 38) has however shown that the androphores are detaclied as free medusiform 

 bodies in liis ' Agalmopsis elegans.' 



The note upon the nomenclature of the parts of the reproductive organs of the Hydrozoa 

 which should have been inserted here (see p. 20) will, I find, take so much more space than I antici- 

 pated, that it must be deferred to the end of the work. 



