ON THE DEVELOPMENT OF LINGULA ANATINA. 77 



ventral body wall. The muscles run forward converging toward 

 each other, and, at about the middle of their course, are 

 attached to the ventrolateral body wall at the posterior dorsal 

 edge of the ventral ganglion, where the fibres of these muscles 

 seem to be broken, so that the part anterior to this point can 

 hardly be regarded as the continuation of the part posterior to it. 

 From this interruption, the muscles continue to proceed forward 

 forming an angle with the posterior limb, and tending still more 

 toward the median plane. They finally secure their attachment 

 on the dorsal body wall at the anterior end of the "Erker," 

 (PI. VII., Fig. 93, PI. VI., Fig. 87). Brooks states that 

 " [the laterales] appear to unite with the dorsal ends of the 

 muscle " h," [occ. ant.'] as no independent ends of similar muscles 

 were visible in a dorsal view " (p. 58) ; but at such stages as 

 Brooks' figures 3, 5 and 6, I find that the muscle has the 

 independent dorsal insertion described above. 



The Obliqui externi (obi. ex.) (Wood-cut B, PL VIIL, 

 Fig. 128). 



These muscles arise from the ventral body wall at the same 

 level as, and on the external side of, the occlusores anteriores. 

 They run between the obliquus internus and the laterales pos- 

 teriorly and dorsally until they are inserted on the dorsal body 

 wall a little posteriorly and ventrally to the obliquus internus. 

 In younger larva? the muscles unite ventrally with the occlusor 

 anterior and it is probable the obliquus externus have at the 

 outset been separated from the occlusor anterior. 



The Obliqui intern i (obi. int.) (Wood-cut B, PI. VIIL, 

 Fig. 128). 



