iv rEKMES 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 end< (dermal 

 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 

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

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

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

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

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

 proceed direct from the stomodanmi. Sometimes, e.g. in the ffir>til/n>n. the 

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

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

 as such disappears. This is the case in many Polyclwcta. 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 tin: British Aiim'lidx. Part I. Nemerteans. 



London, 1872-74. 

 J. v. Kennel. Bcitriiye zur K, ,r//f,iiss der Neim rtiitcn. Arb,'it,',i d. :ooJ. Insfltiits in 



Wiirzburg. Bd. IV. 1878. 

 A. A. W. Hubrecht. Rej>ort on tin' NemerUa, in P^eport on the Scientific licsuUs of 



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



1887. 



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

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



Nematoda. 



A. Schneider. Monographic der Nei'imtnd.fn. Berlin, 1866. 



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



Works and treatises by Meissner, Eberth, Biitschli, Schneider, Leuokart, Claus, 



E. van Beneden, de Man, Rolide, Schulthess, etc. 

 Ontogeny : Biitschli, Gutte, Hallez, etc. 



Gordiidse. 



F. Vejdovsky. Zur Morphologic der Gordiiden. Zeitschr. f. v: ZooL Bd. XLIII. 



1866. 

 The same. Stiidicn iiber Gordiidni. Ibid. Bd. XLVI. 1888. With Bibliography. 



Acanthocephala. 



Carl Baltzer. Zur Kenntniss der Echinvrltiinfhen, in Arcli. f. Naturgeschickte. 



1880. 

 A. Safftigen. Zur Organisation der Echinorhynchen, in Mm'iihoL JuhrlucJi von 



Gegcnbaur. 10 Bd. 1885. 

 Treatises by Greef, Schneider, Andres, etc. 



