198 



The Development of the Eye Muscles in x\canthias 



At a 10 mm. stage the lateral posterior end has become distinctly 

 bilohed, and the more lateral of these lobes bears, in favorably orien- 

 tated sections, a striking resemblance to the visceral portion of the 2nd 

 somite. The disintegration of the epithelial walls of the main portion 

 of the somite continues, while the more dorsal of the two anterior lobes 

 has increased greatly in size. At a 13 mm. stage (Fig. 1) the main 



fci > > 



^ p; ►-; 



O. S. V. 



Tr. 

 S. Ot)l. 



Op. V. 

 Int. Rec. 



Abd. 

 Ga. g. 

 B. Rec. 



Inf. Rec. 



Fig. 8. — Optic vesicle, nerves and eye muscles of an Acautliias embryo, 33 mm. 

 total length. Right side, medial view. The muscles have now nearly their defini- 

 tive position. 



portion of the somite, which is large and globular, is bounded merely 

 by loose .connective tissue which now rapidly fills up the lumen of this 

 part of the somite. There is therefore remaining only the anterior 

 prolongation or dorsal lobe, which consists mainly of elements derived 

 from the median wall. This prolongation now grows rapidly and 

 extends directly forward as an elongate pointed process. Its median 

 dorsal wall is thickened, especially at the posterior end. There, as well 



