246 



I. IKEDA : 



described by the authors, we will here consider the more important 

 question whether all the known fresh-water ncmertincs should proper- 

 ly be regarded, as Bürger 11 docs, to constitute the single genus 

 Tetrastemma, or, as Montgomery and Böhmig believe, to belong to 

 two genera Tetrastemma and Stichostemma. 



The genus Stichostemma was first established by Montgomery in 

 1895, when he described a new fresh-water nemertinc from Berlin 

 (Stichostemma eilJiardi). A year later, the same writer 5 described 

 another new species (St. asensoriatum), belonging to the same genus. 

 In 189S Böhmig redescribed his former Tetrastemma gracensc as the 

 third species of Stichostemma (St. gracensc). The grounds for erecting 

 that new genus were given by Montgomery 35 in 1897, and the distinc- 

 tion he makes between Tetrastemma and Stichostemma, which two genera 

 cover all the known fresh-water nemertincs, will be clear from a compari- 

 son of the diagnoses given by him to each. For Stichostemma he gives : 



" Eyes variable in number, usually more than 4; 9 nerves in the 

 proboscis ; rhynchocoel does not extend to the posterior end of the 

 body ; nephridia extending from in front of the brain to the posterior 

 end of the body ; protandric, hermaphroditic, oviparous." 



And for Tetrastemma : 



" Eyes not variable in number, either 4 single eyes (the rule), or 

 4 double eyes (Ti falsimi, crucia tum) : 10 nerves in the proboscis ; 

 rhynchocoel extends to the posterior end of the body ; nephridia not 

 extending posteriorly behind the oesophagus, dioecious, oviparous." 



Despite Burger's disapproval (1895 and 1904) of establishing the 

 the new genus Stichostemma, Böhmig adopted Montgomery's view in 

 consideration of important differences between the two genera in 



1) Bürger, O,, Die Nemertïrien des Golfes von Neapel etc F. u. Fl. d. Golfes von 

 Neapel, 1895. And also in "Das Thierreich," 19^4. 



2) Montgomery, T.II., Stichostemma asensoriatum n. sp., a Fresh-water Nemertean of 

 Pennsylvania. Zool. Anzeig., Bd. 19, 1895. 



3) Montgomery, T.II., On the Connective tissues and Body-Cavities of the Nemerteans, 

 with Notes on Classification. Zool. Jahrb., Abth. f. Anat. etc., Bd. 10, 1897. 



