HISTORY OF THE SUBJECT. 33 



example of Lineus longissimus, which after four days' captivity produced a cream-coloured young 

 one 18 inches long, and about two thirds of a line or -^th of an inch in diameter. This " young 

 animal " lived about a week after its expulsion. Dr. Gray adds that Dr. Baird had examined 

 the specimen produced, and thinks it very probably the true offspring of the Nemertes. An 

 examination in the British Museum shows that the " young animal," or " tubus cibarius," as the 

 latter lamented observer afterwards named it, is the proboscis, probably, of Cerebratulus angulatus. 



In the c Archiv fur Anatomie' for the same year, Dr. A. Krohn 1 repeats and confirms 

 Muller's observations on the Nemertean Pylidium, and it may be mentioned that this author 

 independently discovered the connection of the structure with a Turbellarian in 1851. 

 The editor (J. Miiller) appends a note to this paper, stating that Micrura of Ehrenberg is 

 identical with Alardus, Busch, and he gives a list w T ith the synonyms of four species of Micrura. 



An elaborate article on the Nemertean Pylidium subsequently appeared in the same volume 

 of the 'Archiv ' (1858) by Leuckart and Pagenstecher, who found two species at Heligoland, viz. 

 P. gyrans of Miiller, and another which they termed P. auriculatum? They traced most minutely 

 the development and relations of the various organs in the embryo of P. gyrans (one of the 

 Anopla), but the origin of the Pylidium itself had hitherto escaped notice. Their species had no 

 style or caudal process after extrusion. Two eyes are developed before the worm separates from 

 the Pylidium. Their account was the best on the subject until the appearance of E. MetschnikofFs 

 recent paper. 



In the same year (1858) W. Stimpson gave in his 'Prodromus' a list, with brief descrip- 

 tions, of the Nemerteans collected in the United States' expedition to the Northern Pacific, and 

 grouped his species under old and new genera, which were arranged to suit the views of the 

 author. His classification is as follows : — 



a. A ventral aperture situated under the head or neck. No eyes. 



a. Lateral fissures on the sides of the head. 



1 . Body of the ordinary form. 



Under this group he places Lineus, Sowerby, Cerebratulus, Renier, Meckelia, Auct. limit., 

 and Serpentaria. The statement concerning the absence of eyes is erroneous. 



2. Body rolled at the edges. — Diplopleura. 



b. No lateral fissures. 



1. Proboscidian aperture terminal. — Taniosoma, n. g. 



2. Proboscidian aperture subterminal. — Valencinia. 



b. No ventral aperture. Eyes two or many. 



a. Eissures or furrows at the margins of the head. — Dic/dlus, n. g., Tetrastemma, 



Hemp, and Ehrenb., Cep/ialonema, n. g., Emplectonema. 



b. Without pits or furrows. 



1. Eyes two. — Diplomma, Dicelis, n. g., Polystemma, Hemp, and 

 Ehrenb., Polina, n. g., Tatsnoskia, Cosmocephala. 



1 'Archiv fur Anat./ 1858, pp. 289—293. 



2 c Archiv fur Anat./ 1858, pp. 569—587, taf. 19. 



