EEPORT ON THE HYDROIDA. 13 



was present on tlie second internode, which was here larger than the others, and carried 

 a mesial as well as a pair of lateral nematophores ; while the continuation of the rachis 

 was arched over the gonangiiim, and had the persistent lateral nematophores of each 

 internode curved backwards so as to be directed towards the convex side of the arch. It 

 would seem to be only on the second internode that a gonangium is borne, and here it 

 takes the place of the hydrotheca, which, had it not l)een suppressed, would have 

 belonged to this internode, while the mesial and lateral nematophores are retained. 



In Lytocarpus saccarius, a species from Ceylon,^ the gonangia are borne near the 

 distal extremity of short ramuli, which are hydrocladia in which the transfoi'mation has 

 been less complete than in the cases described above. In the specimens examined these 

 ramuli were composed each of three internodes. The proximal two internodes carried 

 hydrothecse in all respects like the other hydrothecse of the colony, but in the distal 

 internode the hydrotheca was suppressed, while its mesial and lateral nematophores 

 remained with but little modification, and the solitar}^ gonangium occupied the place of 

 the suppressed hydrotheca. 



In Lytocarpus secundus (PI. XIV.) certain hydrocladia undergo a remarkable modifi- 

 cation in order to become converted into phylactocarps. Their internodes, which are 

 reduced to seven or eight in number, lose their hydrothecse entirely, and carry each a 

 long curved spine-like appendage, which is sujDported on the end of a short process of the 

 internode, and boars a double row of cup-hke nematophores, several nematophores of a 

 similar form being sessile on the internode itself (fig. 5). 



Though no gonangia were developed in the specimens examined, it will scarcely 

 admit of doulrt that the hydrocladia thus modified are true phylactocarps. Analogy 

 would, perhaps, justify us in regarding the spine-like appendages as the mesial nemato- 

 phores of the suppressed hydrothecse, while the lateral nematophores have left no 

 representatives. A comparison of these appendages with the costse of a true corbula at 

 once suggests itself, nothwithstanding their disposition in a continuous series along the 

 mesial line of the rachis, instead of being thrown alternately to the right and left. In the 

 aljsence of gonangia, however, the exact relations of the parts of the phylactocarp to the 

 gonangia, which may yet become developed on it, cannot be ascertained with certainty. 



In the only known forms of Eleutheroplea in which phylactocarps have been detected 

 these structures appear to be in all essential points modified hydrocladia, a number of 

 which combine to form the phylactocarp. In Hippurella annulata, as described by Fewkes, 

 the hydrocladia lose their hydrothecse, and assume a verticillate disposition, arching over 

 the gonangia, which are borne by the stem near their bases. In Callicarpa gracilis, 

 Fewkes, the hydrocladia undergo a similar modification, and, moreover, become dichotom- 

 ously branched." This dichotomous division of a hydrocladium is not without analogy, 



' Linn. Soc. Journ. ZooL, vol. xii. p. 277, pi. xxii. Tlie species is there referred to tlie genus Hnlicornaria. 

 ^ Bull. Mus. Comp. ZooL, loc. cit., p. 134, pis. i., ii. 



