76 ART. 4. — ». YATSU : 



In a ventral view we see the origin of these muselés a little 

 posterior to the ventral ganglion, one on each side of the oeso- 

 phagus. In a dorsal view we see the insertions of these muscles 

 antero-lateral to the anterior dorsal lobe of the liver, a little 

 anterior to the gastroparietal baud and the otocyst (PI. VI., 

 Fi ". 84). In fairly advanced larvae each of these muscles comes 

 to be made up of two halves, median and lateral (PI. VIII., 

 Fig. 128) as in the adult. The lateral half is supposed by 

 Brooks to be the ventral end of the obllquus extemus (I in his 

 terminology). But I found that in larvœ very much younger than 

 those he refers to (Fig. 7, Plate IV.=young sedentary Llngula), 

 the origin of the obliqui externi is distinctly seen a little exterior 

 to the lateral half of the occlusores anteriores. It, however, seems 

 probable that a small part of the anterior occlusor gives rise to 

 the obllquus extemus at the very outset. The occlusores anteriores 

 are divided into two segments, the upper and the lower, equal in 

 length, by the supporting lamella, which projects posteriorly from 

 the dorsal edge of the ventral ganglion (PI. VII., Fig. 94). 



The Ventrales (m. vt.) (Wood-cut B, PI. VIL, Figs. 93, 



94). 



These muscles arise from the ventral body wall, on the 

 median side of the occlusores anteriores, and are made up of a 

 small number of fibres. Running forward along the oesophagus 

 they finally join the transverse arm-muscle. They degnerate toward 

 the end of this stage. 



The Laterales {ht.) (Wood-cut B, PI. VIIL, Fig. 128). 

 The fan-like expanded origins of these muscles are situated 

 a little anterior to the origins of the obllquus médius on the 



