132 McMURRICH. [Vol. IV. 



elucidation of any members of the genus Cerianthus, but in 

 1879 two papers of importance appeared. The brothers Hert- 

 wig ('79) in their studies on the nervous system of the Actini- 

 aria, examined histologically C. vienibraiiaceiis and C. solitarius, 

 and added much to our knowledge of the minute anatomy of 

 these forms, discovering the nervous tissue, describing the 

 arrangement of the muscle-cells correctly, and showing the 

 similarity of all the tissues to those of the other groups of 

 Actiniaria. As regards the general structure, however, they 

 made no advance upon what had been done by Haime, not even 

 correcting some of the errors into which that author had fallen. 



The other paper of 1879 was by von Heider, who treated 

 C. menibranaceiis in as thorough a manner as he had previously 

 done Sagartia troglodytes. Where the Hertwigs are lacking, 

 von Heider excels, giving a more correct account of the ana- 

 tomical features of the species than Haime had done, but. 

 his treatment of the histology is in some points not so com- 

 plete. As regards the anatomy, he showed that the pair of 

 elongated mesenteries are not the most ventral, but that be- 

 tween them is a pair reaching the wall of the siphonoglyphe, 

 but terminating a very short distance below the margin of the 

 groove. These are the ventral directives. He also extended 

 Haime's discovery as to the alternating inequality in length of 

 the mesenteries, by showing that as a rule there is an alteration 

 of gonophoric and non-gonophoric mesenteries, and accordingly 

 divided the mesenteries into three groups ; namely, (i) Filament 

 septa, which are non-gonophoric ; (2) Genital septa ; and (3) Con- 

 tinuous septa, which are represented only by the single pair which 

 reaches the terminal pore. Von Heider describes the Filament 

 septa as giving rise to the acontia, while the Genital septa are 

 provided with mesenterial filaments (craspeda, Gosse). The 

 Hertwigs, in a supplement to their description, after confirming 

 several of von Heider's results, criticise this differentiation of 

 the filaments in the two groups of mesenteries, stating that " in 

 der Beschaffenheit der Mesenterialfilamente zwischen beiden 

 kein Unterschied vorhanden ist." It will be seen that, so far 

 as the structure of the filaments is concerned, this is true also 

 for C. Aniericamts, though there is a slight difference in the 

 arrangement of the different parts of the filament. 



In 1880 a paper by Jourdan ('80) appeared, written, however. 



