THE GONOSOME. 59 



number, and diverge from a common point of attachment, wliilc thcii- wide gastric cavities, after 

 contracting below, communicate here with one another and with the tuljular cavity of the 

 blastostyle. 



I have never been able to discover any direct relation between these gonangial liydranths 

 and the generative functions of the hydroid. The ova, so far as I can determine, seem to be 

 produced in the usual way in a sporosac which springs from the blastostyle, and are tiicn dis- 

 charged into a chamber formed by the gubernacular sac (c), the sporosac itself entirely disappearing 

 after the loss of its contents. In the sort of internal marsupium thus formed the ova pass 

 through certain stages of their development before their ultimate liberation as planulae through 

 the summit of the gonangium, which takes place, probably, after the disappearance of the 

 gonangial hydranths. 



I may here mention a very singular body, whose exact significance I have never been able 

 satisfactorily to determine, and which may he seen in the female gonangium of Aiifennularia 

 antennina, where it is of frequent occurrence. It is always found floating free in the cavity of 

 the gonangium, along with the ova which had escaped from the ruptured gonopiiores, and 

 resembles an imperfectly developed medusa, with a large and apparently imperforate manubrium, 

 but with its umbrella closed, and without any trace of gastrovascular canals, the walls of the 

 umbrella being separated from the manubrium by a considerable space, which is filled with 

 a clear fluid. It may be compared to a free sporosac ; but it is much smaller than the ordinary 

 sporosacs of the AniennuJaria ; and I have never observed in it any trace of generative elements. 

 It is possibly an undeveloped sporosac, produced, like the perfect sporosacs, as a bud from the 

 blastostyle, and becoming separated at an early stage ; but I can offer no decided opinion either 

 as to its origin or its ultimate destination. It may be a parasite, though it is not easy to reconcile 

 its peculiar structure with this view. 



In almost every case the gonangium, when present in the Hydroida, is destitute of any 

 fiuther covering. In certain hydroids, however, belonging to the family of the Plumiduriclce, 

 the gonangia are developed in groups, and each group is contained in a common receptacle, 

 which confers upon the hydroid in which it exists a very striking and characteristic feature. 

 This receptacle must be carefully distinguished from a proper gonangium, with which, indeed, it 

 has been confounded in various descriptive works on the Hydroida. It will therefore be very 

 convenient to give it a special name, and I have already proposed for it the term corbula, 

 suggested by its basket-like form.^ 



In Aglaophenia phima the corbulas (woodcut, fig. 30, D) may be plainly seen to be meta- 

 morphosed ramuli. The peculiar metamorphosis of a ramulus, which results in the formation 

 of a corbula, consists here in the suppression of the hydrothecse, accompanied by the development 

 on each side of the ramulus of numerous oval, hollow, alternately placed leaflets ; each leaflet 

 consisting of a diverticulum from the coenosarc of the ramulus, invested by a continuation of 

 the general perisarc. 



In the earliest stages of these leaflets (A, a) their edges are entire, but they soon become deeply 

 serrated by the formation of hollow tooth-like processes, more especially upon the edge which is 

 turned towards the distal extremity of the ramulus. Upon the proximal edge of the leaflet these 

 processes usually remaii in an imperfectly developed state, though they are occasionally equally 



' ' Proc. Roy. Soc. Ediu.,' 1858. 



