THE GONOSOxME. IT) 



the name of " mccoiiiclium." It is perforated at its summit, and tlic perforation is surrounded 

 by a distinct circular canal, which receives four radiating canals, which open into it by small 

 bulbous expanions (woodcut, fig. 15, C). We thus find almost entirely the conditions of a medusa 

 — a medusa, however, which never divests itself of its ectotheca, and accordingly never becomes 

 free, while the spadix remains as a simple caecal diverticulum, and the codonostome is reduced to 

 a mere perforation of the mcsotheca, this last exhibiting but the faintest traces of contractility, 

 and being quite incapable of acting as a locomotive umbrella. 



From the sporosac of Tuhulnria hidivisa it is thus but a single step to the true phaneroco- 

 donic gonophore, such as we find in Corymorplia nidans, or Syncoryne cximia, where the 

 mcsotheca assumes the condition of a contractile locomotive umbrella, with a well-developed 

 codonostome and velum, and, the manubrium now becoming perforated by a mouth, the gono- 

 phore is no longer dependent on the trophosome for its nutrition, but can l)ccoine free and lead 

 an independent life in the open sea (woodcut, fig. 15, D). 



The typical and ordinary condition of the spadix is that of a hollow cylindrical or clavate 

 body, occupying the axis of the adelocodonic gonophore. Occasionally, however, it departs from 

 this condition and becomes more or less branched, as in Cordylnphora lacustris (PI. Ill), 

 Plumidaria jnnnata, Laomedea caliculafa, &c. 



The gastrovascular canals in the adelocodonic gonophore may, as we have already seen, be 

 either entirely suppressed or present the condition of simple, short, blind tubes, radiating from 

 the base of the gonophore, or be continued from this point as fully developed radiating canals to 

 the distal extremity of the gonophore, where they become united by a circular canal. In certain 

 free medusa3 [WUlia, Chidoncma — PI. XVII) the radiating canals subdivide before reaching the 

 circular canal. 



The usual condition of the adelocodonic gonophore is that of a simple, more or less spherical 

 or oval sac. In Eudendrium, however, the male gonophores present the form of a simple sac 

 only at first ; for by the time that their contents have approached maturity, new spermatogenous 

 tissue becomes apparent between the endoderra and ectoderm of their supporting peduncles, and 

 these two membranes thus become separated from one another so as to form a second sac inune- 

 diately below the first, while a third may in the same way be formed below the second, the gono- 

 phore thus acquiring the peculiar moniliform or polythalamic conformation characteristic of this 

 genus (woodcut, fig. 16). It will beat once apparent that the separate chambers presented by this 

 peculiar form must not be regarded as so many distinct gonophores ; the whole moniliform series 

 ought rather to be viewed as a simple adelocodonic gonophore, in which the perigonium is not 

 uniformly separated from the spadix by the intervention of the spermatogenous tissue, but 

 remains at intervals permanently adherent to it. Among the planoblasts an entirely analogous 

 })henomenon occurs in a Sarsia-X^Q medusa of unknown trophosome, which I captured in the 

 towing-net on the south-west coast of Ireland (woodcut, fig. 17). In this the manubrium, which is 

 extraordinarily extensile, and can be projected to a great length beyond the umbrella, was enlarged 

 at distinct intervals by the development of the generative elements between its ectoderm and 

 endoderm. The specimen captured was a male, and the manubrium, when extended, presented, 

 by the mode in which the spermatogenous tissue was developed in its walls, five elongated 

 cylindrical enlargements, separated from one another by long thin intervening portions, in which 

 the ectoderm and endoderm of the manubrium continued in direct contact with one another, no 

 generative elements being there developed. The spermatogenous mass which occupied the free 



