iv VERMES LITERATURE 283 



with the nervous system localised and condensed in 4 micromeres, the rudiment of 

 the mesoderm in 4 other micromeres, and the rudiment of the whole endodermal 

 enteric system in the 4 macromeres. 



Development of the Intestine. The intestine of the worms consists as a rule of 

 three parts of different origin the fore-gut, the mid-gut, and the hind-gut. From 

 the" endodermal archenteron of the gastrula only the mid-gut is derived. At an 

 early stage in larval life an anterior ectodermal invagination, the embryonic or larval 

 oesophagus or the stomodieum, becomes connected with it, while a similar invagina- 

 tion at the posterior end yields the proctodseum. "While the proctodaeum becomes in 

 a direct manner the hind-gut, which is often very short, the fore-gut does not always 

 proceed direct from the stomodseum. Sometimes, e.g. in the Hirudinea, the 

 stomodaeum disappears and a new oesophagus arises independently in its place. 

 Sometimes the definitive oesophagus begins to form out of the stomodaeum which 

 as such disappears. This is the case in many Polychceta. The musculature 

 of the fore-gut, which is often very strongly developed as the pharynx, seems every- 

 where to be formed from the cephalic portion of the mesodermal or germ streaks. 

 The origin of the muscular wall of the mid-gut and its endothelium, where this is 

 present, from the visceral layer of the mesodermal streaks has already been described. 



Literature. 



Nemertina. 



W. C. M'Intosh. A Monograph of the British Annelids. Part I. Nemerteans. 



London, 1872-74. 

 J. v. Kennel. Beitrdge zur Kenntniss der Nemertinen. Arbeiten d. zool. Instituts in 



Wurzburg. Bd. IV. 1878. 

 A. A. W. Hubrecht. Report on the Nemertea, in Report on the Scientific Results of 



the Voyage of H. M.S. Challenger. Zoology. Vol. XIX. Part LI V. London, 



1887. 



Treatises by Quatrefages, Hubrecht, Oudemans, Moseley, L. v. Graff, Dewoletzky. 

 Ontogeny : Hubrecht, Salensky, Gotte, Barrois, etc. 



Nematoda. 



A. Schneider. Monographic der Neinatoden. Berlin, 1866. 

 R. Leuckart. Die Parasiten des Menschen. New edition in preparation. 

 Works and treatises by Meissner, Eberth, Biitschli, Schneider, Leuckart, Glaus, 



E. van Beneden, de Man, Rohde, Schnlthess, etc. 

 Ontogeny : Biitschli, Gotte, Hallez, etc. 



Gordiidse. 



F. Vejdovsky. Zur Morphologic der Gordiiden. Zeitschr. f. w. Zool. Bd. XLIII. 



1866. 

 The same. Studien iiber Gordiiden. Ibid. Bd. XL VI. 1888. With Bibliography. 



Acanthocephala. 



Carl Baltzer. Zur Kenntniss der Echinorhynchen, in Arch. f. Naturgeschichte. 



1880. 

 A. Safftigen. Zur Organisation der Echinorhynchen, in Morphol. Jahrbuch von 



Gegenbaur. 10 Bd. 1885. 

 Treatises by Greef, Schneider, Andres, etc. 



S+ 



