HEAD SOMITES AND EYE MUSCLES IN CHELYDRA 163 



steht und vom Nervensystem vollig unabhangig auftritt (p. 343, in 

 regard to anlage of N. abducens). 



In der Entwicklungsgeschichte des Oculomotorius ist ebenso wie in 

 der Abducens die Tatsache bemerkenswert dass die urspriingliche Ner- 

 venanlage als unmittelbare Fortsetzung der Muskel- oder Somitenanlage 

 dem Nervensystem nur angelagert ist und erst sekundiir Beziehungen 

 zu demselben durch die von dorther in die Anlage hineinwachsenden 

 Nervenfasern gewinnt (p. 363). 



The relation of the abducent nerve to the brain and to its 

 muscles, at the time of its first appearance in Chelydra, has 

 already been discussed. Contrary to Filatoff's opinion, the nerve 

 does not arise in continuity with the developing muscles. Con- 

 nection with the muscles is acquired later. Moreover, the abdu- 

 cent nerve is to be interpreted as formed by the direct outgrowth 

 from the brain of several deUcate filaments, which unite to form 

 a bundle that is easily seen. In the early stages of Chelydra 

 it is only on superficial examination that the filaments which 

 connect this bundle with the brain may be overlooked. 



Similarly the oculomotor nerve, when first found in the present 

 study, had no connection with the first head somite, but could 

 readily be followed to the brain tube. In the 10-mm. embryo, 

 where the cihary ganghon appears as an accumulation of cells 

 at the distal end of this nerve; it still has no connection with its 

 muscles. At 11 mm., however, the nerve extends beyond the 

 ventral border of its ganghon and connects with the Mm. recti 

 superior, inferior and mediaHs. Later it connects with the M. 

 obhquus inferior, and eventually it becomes separated from the 

 ciliary ganglion except for a branch which forms the short root 

 of the ganglion. Filatoff's conclusions, therefore, are not appli- 

 cable to Chelydra. 



LITERATURE CITED 



Balfour, F. M. 1878 Development of Elasmobranch fishes. 



BojANUS, L. H. 1819 Anatome Testudinis Europaeae. 



Bratts, H. 1897 Beitrage zur Entwicklung des Muskel- und Peripheren Ner- 



vensystems der Selachier. Morph. Jahrb. Bd. 27. 

 Corning, H.K. 1900 Ueber die Entwicklung der Kopf-und Extremitaten Mus- 



kulatur bei Reptilien. Morph. Jahrb. Bd. 28. 



