12 



HYDROIDA 



of the tentacles is simple, with no central cavity, and with a thin supporting lamella without any 

 particular thickening. In the endoderm we must distinguish between an oral portion, abounding 

 in mucous gland cells, and the gastral portion proper. The colonies develop no calcareous skeleton". 



It is questionable, as is also pointed out by Kuhn (1913), whether it is justifiable to maintain 

 the Corynidac and the Pennariidae as two distinct families. Stechow (1913) states that "das gleich- 

 zeitige Vorkommen geknopfter und fadenformiger Tentakel ein vorziigliches Merkmal fiir das Bestim- 

 uieu ist"; simultaneously, however, he ranks the genera Acaulis and Clavatella with the Corynidac, 

 though, having tentacles both capitate and filiform, they should, from this main characteristic, be 

 reckoned among the Pennariidae. Also as compared with the Tubulariidae, the limitation of the Pennarii- 

 dae makes some difficulty. Thus Bonne vie (1899) e. g. classes Hctcrostcphauus among the Tu- 

 bular iidac in spite of the fact that the species is provided with capitate distal tentacles. Stechow 

 (1913), on the other hand, as well as Broch (1911), ranks this genus with the Pennariidae. I regret 

 that I am in lack of material for a more thorough inquiry into the Pennariidae; it is not unlikely 

 that the anatomical structure of the polypes might afford safer holds for the judging of this group of 

 hydroids than the merely outward morphological characters. 



The Corynidac form a very central group, with which all the other groups of the section of 

 Capita ta, stated by Kuhn, are likely to have originated. — At the first glance it may appear as if 

 one of the genera A/ouocorync has got nematocysts heterogeneously developed, so as to show, be- 

 sides oviform or globular capsules, partly also long, narrowly oval ones. That this is not the case, is ascer- 

 tained by a careful study of material of Monocoryne gigantea (Bonne vie) collected in the 

 Trondhjemsfjord. Partly all the nematocysts of this shape are discharged, and partly developmental 

 stages of other nematocysts than oviform ones are not traceable. It is, therefore, obvious that, in 

 being discharged, the oviform nematocysts assume a narrowly oval shape. The apparent dimorphism 

 of the nematocysts would otherwise have been greatly interesting as a connecting link with Myrio- 

 t/nla, and would have been likely to support the supposition of Bonne vie (1899) of the derivation of 

 the last-mentioned genus from the Corynidac through Monocoryne. But as a matter of fact, the large 

 Monocoryne gigantea shows the anatomical structure of the true Corynidac. Swenander (1903) mentions 

 that its tentacles are coalesced at the basis; this statement, however, only holds good for the ectoderm, 

 which in several places appears to be stratified; the endoderm, as far as the single tentacles are con- 

 cerned, continues, wholly surrounded by the ectoderm, to the supporting lamella. Monocoryne gigantea 

 presents another peculiarity which the inquirers have hitherto obviously failed to notice; the indivi- 

 duals are hermaphrodite, in a most peculiar way. Not only we find in a single individual sheer female 

 and sheer male gonophores; but among these also occur several gonophores containing, besides large 

 ova, also sperms and spermatocytes of all stages. The gonophores of this species are reduced to 

 cryptomedusoids. 



In the internal structure of the polype of the Corynidac our attention is fixed on a great ac- 

 cumulation of mucous gland cells in the endoderm next to the orifice. Here are densely accumulated 

 a lot of cells, whose affinity with Delafield's haematoxyline make them very conspicuous on material 

 well preserved. This concentrated glandular zone is found still more strongly marked in the Myrio- 



