178 



tedon rosacea Norm., the two latter on the rarer A. phalangium 

 Müller 1. 



AU writers on the anatomy of Myzostomes — Lové n 2, Sem- 

 per^, V. Graffa, Beard^, Nansen^, Prouho' — assume that the 

 large branching organ containing ova in various stages of matures- 

 cence is the ovary. This organ is lined with peritoneal epithelium 

 and opens on either side by means of a number of conduits into the 

 median »uterus«. The uterus, a capacious receptacle in the mid dorsal 

 line, opens posteriorly into the cloaca very near the anal orifice. Most 

 writers believe that the ova develop in situ from peritoneal cells lin- 

 ing the coecal ramifications of the ovary; v. Graff, however, inclines 

 to the more improbable view that the ova arise from connective tissue 

 elements. 



Nansen, while sharing with other investigators the interpreta- 

 tion of the ramified organ as an ovary, pointed out the existence of 

 a pair of very small bodies (in some species two pairs) lying one on 

 either side of the main stem of the gut near the middle of the body. 

 He regarded these structures (»problematical organs«) , which he de- 

 scribed as consisting of minute deeply staining cells , as abortive ova- 

 ries, and supposed that they had lost the power of producing ova when 

 this function was transferred to the general peritoneal epithelium lin- 

 ing the coeca of the ramified organ. 



A closer study of these »problematical organs« enables me to state 

 that they are in no sense abortive, but the only true ovaries of Myzo- 

 stoma. Under a high magnification they are seen to be solid prolife- 

 rations of the peritoneal epithelium over a very restricted area. In the 

 string-like masses of minute cells numerous caryokinetic figures may 

 be detected, especially in young Myzostomes. These divisions finally 

 result in the formation of groups of three cells each. In each group 



1 At Naples I have not been able to find M. Bucchichii, a species described 

 by V. Wagner (Zool. Anz. No. 255. 1887. p. 363— 364)from a single specimen found 

 on A. rosacea near the Isle of Clemente. 



2 S. Lovén, Myzostoma cirriferum Leuck., ein parasitischer Wurm. Arch. f. 

 Naturg. 8. Jhg. 1842. p. 306-314. Tab. VIII. 



3 C. Semper, Zur Anatomie und Entwicklungsgeschichte der Gattung Myzo- 

 stoma Leuck. Zeitschr. f. wiss. Zool. IX. Bd. 1857. p. 48—64. Tab. III, IV. 



4 L. Graff , Das Genus Myzostoma (F. S. Leuckart). Leipzig 1877. p. 1—82. 

 Tab. I— XI. 



5 J. Beard, On the Life History and Development of the Genus Myzostoma 

 (F. S. Leuckart). Mitth. a. d. Zool. Stat. Neapel. V.Bd. 1884. p. 544—580, Tab.XXXI, 

 XXXII. 



6 F. Nansen, Bidrag til Myzostomernes Anatomi og Histologi. (English Re- 

 sumé.) Bergen 18&5. p. 1—80, Tab. I— IX. 



^ H. Prouho, Sur deux Myzostomes parasites de V Antedon phalangium (Mül- 

 ler). Compt. Rend. 1892. p. 846—849. 



