REPORT ON THE HYDROIDA. 23 



tlieca ; liydrocladia alternate, rather more than one-tenth of an inch in length, arising one 

 from every internode of the stem close to the base of a hydrotheca. Hydrothecfe deep, 

 conical in front view, cylindrical in profile, adnate by somewhat more than half their 

 height to the supporting internode, flanked on either side by a short tooth-like process, 

 which carries a long lateral nematophore ; a single mesial nematophore borne by the 

 hydrothecal internode at the proximal side of the hydrotheca, and another at its distal 

 side in the hydrocladia, while in the stem the single mesial nematophore is replaced in 

 the distal portion of each internode by a pair of lateral nematophores. 



Gonosome. — Female gonangia borne along the stem, each springing by a very short 

 peduncle from a point opposite to the origin of a hydrocladium, large, ovate with 

 truncated summit, carrying from base to summit along one side a single linear series of 

 nematophores. 



Male gonangia developed in the same colony with the female, and borne exclusively 

 by the internodes of the hydrocladia, springing by a short peduncle from the internode at 

 the proximal side of its hydi'otheca, very much smaller than the female, crescentic in 

 form, destitute of nematophores, and with rounded summit curved towards the 

 supporting internode. 



Plumularia armata is a small and delicate Hydroid. The condition of the gonosome 

 is very exceptional. The nematophores, which are developed on the outside of the female 

 gonangium, constitute in themselves a veiy unusual and striking feature. These extend 

 in a continuous series along the course of the blastostyle, with which they communicate 

 through perforations in the chitinous walls of the gonangium. In order to allow of this 

 communication, the blastostyle is thrown out of the axis of the gonangium, and lies 

 against the inner surface of its walls, immediately under the series of nematophores. 



In Sciurella indivisa of the present Eeport we also find the gonangium carrying 

 numerous nematophores. Here, however, the nematophores are not arranged in a single 

 series, but form symmetrically disposed groups. 



Striking, however, as is the development of gonangial nematophores in these instances, 

 it is only an extreme case of what occurs in several other Eleutheroplean Plumularidae, 

 as in Plumularia catharina and allied species, and in Antennularia fascicularis, and the 

 two species of Scliizotricha described in the present Report. In all these a pair of 

 nematophores is developed from the base of the gonangium, and there communicates 

 with the proximal end of the blastostyle. 



Another very exceptional, though by no means unique character, is found in the 

 presence of both male and female gonangia in the same colony. These chfier not only in 

 form but in situation. The large ovate female gonangia, with their series of parietal 

 nematophores, ai'e borne exclusively on the stem, which, like the hydrocladia, is 

 composed of a series of hydi-otheca-bearing internodes, while the very much smaller 

 crescentic male gonangia are confined to the hydrocladia. 



