22 HYDROIDA 



of species with Myriothela, there tells indeed little in favour of raising it to a distinguishing mark 

 between two subfamilies of the Tubiilariidac. As far as finally the development of the periderm is 

 concerned, this is a gradual character showing many transitions, to which no importance can be 

 attached as a distinguishing mark between two subfamilies. 



Gen. Tubularia Linne. 



"Hydroids most frequently forming colonies, the hydrocaulus being surrounded by a stiff and 

 chitinous perisarc. The polyps are radially symmetrical, having two main circles of tentacles, a proximal 

 (basal) whorl of long tentacles leaning on a mesogloeal ring in the trunk of the polyp, and a distal 

 whorl with short tentacles round the mouth. The tentacles are also in the actinula filiform.' The gono- 

 phores are generally borne on blastostyles; the gouangia spring from the trunk of the polyp between 

 the two whorls of the tentacles". 



The gonophores are, in this genus as in most other genera, sometimes medusoid, sometimes 

 more or less reduced. The species producing free medusae have been grouped b)- many authors as a 

 genus of their own, Hybocodo)i. In this case as in others, the question then arises where the line is to 

 be drawn. While in species as Tubularia pulclier {Scemundsson) the medusa breaks away, the fully 

 developed medusoid gonophore in Tubularia re galis Boeck, as far as is known to us, never voluntar- 

 ily relinquishes its sessile existence. If we follow Kiihn (1913), as might seem right, we get into a 

 dilemma, having to refer the female of Tubularia regalis to Hybocodon^ while the male, having crypto- 

 medusoid gonophores (Broch 1915), must remain in the genus Tubularia. Only this should be suffi- 

 cient to show the error of turning the organisation of the gonophores to account as fundameutum 

 divisionis. No doubt, it is wrong to set up Hybocodon as a particular genus of hydroids, and the same 

 is certainly the case with the genus Auliscus set up by Ssemundsson (1899), the medu.sae of which 

 as we are going to see, are scarcely particularly distinguished as compared to the other Hybocodon- 

 medusae. 



Tubularia pulcher (Sremundsson). 

 1899 Auliscus puhlirr Stem unds son, Zoologiske Meddelelser fra Island, p. 425, Tab. IV. 



"Colonies, the hydrocauli of which are uj? to 50 mm. long, unbranched, and separated down to 

 the reptant hydrorhiza. The stalk is covered with a brown perisarc, which is thick at the base, but 

 upwards against the polyp narrowing periodically and at distinct intervals, so that the stalk gets an 

 appearance approximately articulate; the spaces between the transverse striae, brought about in this 

 way, attain their greatest length in the middle part of the stalk, being here 13 mm. long. The upper 

 portion of the stalk is provided with a thin perisarc, widening funnel-shapedly into a thin collar 

 under the polyp. The polyp is fitted oiit with a basal circle of 24 — 30 tentacles, about 5 mm. long; 

 the distal tentacles, about 30, arc j)laced, densely crowded, in a narrow belt, consisting of several rows, 

 round the orifice, and attain a length of a little more than i mm. 



The gonophores develop into free Ilybocodon-ra^Awssje. with gemmation on the bulb of the 



' The tentacles of the actinula may be swollen at their tips (conip. Allnian 1872) but never show the dense accumula- 

 tion of stinging cells here, which is so characteristic in the truly capitate tentacles of the section Capitata. 



