58 



MORPHOLOGY. 



Fig. 29. 



time affords a support for the gonophores after they have become extracapsular. Two or tliree of 

 these extracapsular gonophores, in different stages of development, may Ije usually seen, borne 

 each by a short peduncle upon the opercular summit of the blastostyle, with whose cavity that 

 of their spadix freely communicates through the tul)ular axis of the peduncle. 



While the gonophore is still contained within the gonangium, the mesotheca has become 

 developed in it, and in the more advanced ones {d") the rudimental tentacles may be seen thrown 

 back in their walls in the form of a little star. 



That the bodies now described belong to the class of adelocodonic rather than to that of phane- 

 rocodonic gonophores must, I think, be admitted. In all essential points, except in the presence of 

 entacles developed from the mesotheca, they agree with the gonophores of Tuhidaria iudivisa, which 

 must certainly be classed among the adelocodonic forms, notwithstanding their possession of a 

 well-developed mesotheca and gastrovascular canals. In both the 

 aperture of the mesotheca is reduced to a mere perforation, and in 

 neither is the mesotheca ever developed as a locomotive organ. 



It nuist also be borne in mind that, when planoblasts are 

 produced in the Campmudarince, they are in almost every instance 

 blastochemes ; in other words, they belong to the type in which 

 the generative elements are produced, not dii'ectly, as in Gono- 

 tliyraa, between the ectoderm and eudoderui of the manubrium, 

 but are formed in special zooids developed from some pai'ts of the 

 gastrovascular system ; Leptoscyplms tenuis, Allm.,^ affording the 

 only known exception to this rule. 



The extracapsular gonophores of Gonotliyraa Love id are thus 

 of no little interest in the morphology of the Hydroida, and it will 

 be found convenient to speak of them under a special name. Their 

 resemblance to a pomegranate, or perhaps still more obviously to 

 a poppy-capsule, with its sessile stellate stigma, will instantly strike 

 us ; and it is this comparison which has suggested to me the name 

 of meconidium ^ by which I have elsewhere found it useful to 

 designate them. 



A very remarkable feature, which one is at first sight tempted 

 to place in the same category with the formation of meconidia, 

 but which is in reality of an entirely different significance, is pre- 

 sented by Halecium halecinum. In this hydroid there is borne 

 upon the summit of the female gonangium, in a situation precisely 

 similar to that of the meconidia of Gonothyroea Love/ii, a pair of 

 hydriform bodies (woodcut, fig. 2Q d). These bodies present no 

 appreciable difference by which they may be distinguished from the 

 ordinary hydranths of the trophosome. They are of an elongated 

 oval form, with the mouth situated on the summit of a short conical 

 hypostome, which is siUTounded by a circle of filiform tentacles. They are always two in 



^ "Notes on the Hydroid Zoophytes," 'Ann. Nat. Hist.,' Nov., 1859. 



^ A diminutive noun, formed from /jh'ikuiv, a poppy. "Notes on the Hydroid Zoophytes,'"' 'Ann, 

 Nat. Hist.,' August, 1859. 



Gonangium with gonangial 

 hydranths in Halecium hale' 

 cinum, 



a, a, Gonangium ; h, h, blas- 

 tostyle ; r, gubernacular mem- 

 brane, still confining the ova, e, e, 

 which are here in an advanced 

 ' stage of development, the proper 

 gonophore having become ab- 

 sorbed after discharging its con- 

 tents ; d, gonangial hydranths. 



