ACTINIAKIA 



to decide the size of the nematocysts in the actinopharynx, as it is very difficult to get positive maceration- 

 preparations of the little actinopharynx. Spirocysts appear to be absent here. 



In a publication (1913) Kerb discusses the transversal partition of Gonactinia, and verifies as myself 

 (1893) that the reproductive organs develop as well in the distal as in the proximal dividing pieces. Further- 

 more he means having found that also the proximal piece divides transversely. I am, however, of opinion 

 that his experiments are not thorouglily proving, Kerb having started not from a chain of 3 indiduals, but 

 only from one of 2 individuals. Under such circumstances it is therefore possible that the proximal piece 

 dividing a second time was a middle piece, and not the primitive proximal piece of the chain. A. chain of 3 

 individuals is namely to my mind very common in Gonactinia. (Carlgren 1904 p. 145. Kerb has evidently 

 overlooked this paper). Thus of 10 transversely dividing specimens of Gonactinia, collected by Sars himself, 

 no less than half the specimens were in tridivision, and yet Sars himself states having observed only a 

 single one. In the above-mentioned paper I have tried to explain the reason why the chain of three indi- 

 viduals is overlooked. Besides it is possible that under very favourable circumstances the partition takes 

 place so rapidly that the proximal piece is dropped before the middle piece is erected. In order to get a 

 binding evidence that the most proximal piece divides again, it is necessary to follow the development of 

 the division in a chain of 3 individuals. The experiments of Kerb only show that a proximal part is able to 

 divide a second time, but leave undecided, whether it was a primitive proximal part or a middle piece 

 that divided transversely. 



Genus Sideractis Dan. 



Diagnosis: Gonactiniidae with weak muscularity, without sphincter. Column and actinopharynx 

 with weak, ectodermal, longitudinal muscles extending into the indistinct pedal disc. Column with spiro- 

 cysts, but without nematocysts. Tentacles hexamerously arranged at least to the stadium of 24 tentacles, 

 conical, of ordinary length, the inner ones considerably longer than the outer ones. Apex of the tentacles 

 hemispherical, smooth, with batteries of large, stinging capsules, the peduncle of the tentacles with small, 

 papilliform elevations which also occur, though less numerously, on the oral disc and on the distal part of 

 the column. Oral disc conical. Actinopharynx longitudinally sulcated, without differentiated siphonogly- 

 phes. 6 pairs of perfect mesenteries with filaments, and fertile. Variable numbers of weak mesenteries, sterile 

 and without filaments. Parieto-basilar muscles weak. Typical nematocysts absent. 



The above diagnosis of the genus completely differs from that given by Danielssen 1890. Above 

 everything I must emphasize that the statement of Danielssen that the circular muscles are mesogloeal, 

 is wrong. Besides, the description of the anatomical conditions by Danielssen is on several points erro- 

 neous and very incomplete. After an examination of well preserved material, compared with that of Da- 

 nielssen, the genus turned out to be a very primitive form belonging to the family Gonactiniidae. 



Danielssen has established the genus as a separate family, Sideractidae, which in his opinion 

 would be related to the family Boloceriidae. Also Me. Murrich (1893 p. 153) adopts this opinion. This is, 

 however not the case, as the following description will clearly show. Verrill (1899 p. 143, 144) declares 



