HYDROIDA 45 



polyps are provided with a riii<j of stingino- cells above the base of the tentacle. The stolons form a 

 network of anastomosing tnbes. 



The gonophores are eumednsoid with a nidinientary spadix and with the generative cells 

 placed along the four radial canals. The colonies are bisexual. 

 Material: 



Greeidand: Kgedesminde (on Tcllina calcarca). 



The Kara Sea ("Dijmphna"). 



Mouobrdcliiuiii parasitiiiii is indigenous to the middle parts of the literal region far to the north. 

 It is recorded frt)ni Spitzbergen, the Kara Sea, the White Sea, and the west coast of Greenland 

 (Text-fig. L). 



Family Bougainvilliidae. 



Hydroids forming colonies with pol)-ps fusiform or capitate, whose oral portion is conically 

 pointed. The stinging cells are small and rodshaped. The tentacles, which are filiform, are placed in 

 a main whorl round the polyp; the stinging cells are equally distributed all over the surface of the 

 polyps or in less distinct transverse belts round them. The 23olyps are quite naked or surrounded by 

 a jellied, lithe, and pliable pseudohydrotheca below the tentacle whorl. The endoderm is differentiated 

 into an oral portion, consisting of indifferent small-nucleated cells between which occur a large number 

 of mucous gland cells, and the jriroper gastral portion ; the limit is formed by the tentacle whorl. The 

 colonies have no calcareous skeleton. 



The diagnosis states for the family the same range as was practically already given b\- Bon- 

 ne vie (1899), wdiom the later authors have generally followed. Kiihn (1913) divides the family into 

 three subfamilies, two of which, Ilydractiuiiiiac and Atractylinae^ are represented in our northern seas. 

 The main distinguishing mark stated by Kiihn is that /fydracfiiiiiiiac are stated to have a vigorous, 

 crustformed skeleton, while ^ifractyliiiar, on the other hand, ha\-e hydrocauli covered with periderm. 

 Howe\cr, this character does not seem to be of the importance Kiihn attached to it. In young 

 colonies the stolons have not coalesced into a crust, and the development of the skeleton is not parti- 

 cularly vigorous. There is even every probability that several species of Stylactis do not at all assume 

 such crustformed skeleton-formations, even when advanced in life. On the other hand, we also know 

 species of Hydracti)iiuiat\ in w liich the hydrocaulus covered with periderm has been reduced to a mere 

 minimum. The character, therefore, must be characterized as a merel>- gradual one, and can hardh- be 

 turned to account as fundamenlum di\isionis for higher groups. 



A very different interest is attached to the peculiar occurrence of pseudoluxlrothecae met with 

 in the Bo2igaiiivilliidai\ I set aside the socalled pseudohydrothecae of Clathrozoon (the subfamily Hy- 

 droccrati)iiii(u\ stated by Kiihn 1913); in fact, this group is not yet so well known that we arc able 

 to judge of it entirel}-, and its "pseudohvdrothccae" do not seem to form such a parallel with the for- 

 mations of the thecaphores as those found in certain other Botigainvil/iidat\ namely in Pcrigo- 

 iii)iuts. In this species the ectoderm of the pol\p has secerned a jellied pseudohydrotheca, which has 

 coalesced with the pol\ p along its distal margin, and to which the basal portion of the supporting 



