126 



HYDROIDA II 



which is ellipsoidal in section. Even though this form may predominate in many colonies, it is 

 nevertheless far from constant; a very high degree of variation may normally be observed even 

 within a single colony (fig. LXV c k). We often find, on one and the same branch, gonothecse with 

 two points, others with but one, and some with none at all. (This applies, of course, only to acrocyst- 

 bearing, i.e. fully developed, gonothecae; those shown were all provided with acrocysts.) Now while 

 in some colonies the two-pointed gonothecae are numerically predominant, though it is extremely 

 seldom that they are practically supreme, this "normal" form of gonotheca is in the minority in other 

 colonies, where on the contrary the great majority are of the one-pointed type; the entirely spineless 



Fig. I<XV. Sertularia cupressina. 



a Distal hydrothecae of a branch of a colony from the western coast of South Jutland. b Proximal hydrothecae from 

 the same branch. c Distal hydrothecae of a branch of a colony from 6 miles N. by W. of Store Kalso. d Proximal 

 hydrothecae of the same branch. e g Gonothecse from the same colony as a and b. hk Gonothecae from the 



same colony as c and d. (X 40). 



gonotheca again is not represented to any considerable number in any colony in the material, and 

 must be reckoned as an exception of more or less frequent occurrence. The mentioned variations 

 in the gonangia throw a doubtful light upon unicarinate forms such as Sertularia Birulce Schydlow- 

 sky, where the trophosome, according to the descriptions given, does not differ from that of Sertula- 

 ria cupressina; the species should doubtless be withdrawn, but as it is not represented in the material, 

 further investigation should be made before the point is decided. 



After the investigations described, it is impossible to maintain the distinction between Sertu- 

 laria cupressina and Sertularia argentea. The distinction in question, which was originally made from 

 a very restricted material, has since only been retained on the strength of superficial studies, as is 

 shown by the case of the asymmetrically developed teeth above mentioned. And it is just such super- 

 ficial investigations which have led to this superfluity of species into which the genus is still divided. 



Sertularia cupressina should best be characterised as a boreal species capable of penetrating 



