882 



THE AMERICAN NATURALIST 



[Vol. XL 



tion of these muscles, I have made a diagram (Fig. 4) to show 

 their position in the body of the animal, and have designated 

 those of the left side in the order of their insertion passing from 

 left to right, by the letters a, h, c, and d, and the corresponding 

 ones of the right side, also in the order of their insertion passing 

 from right to left, by the letters a',h',c', and d'. Muscle a, which 

 has a diameter of about 35 jw just before branching, is as large as 

 any of the gill retractors. It is fastened to the basal region of the 

 left gill by three branches. One is inserted in the lateral, another 

 in the dorso-lateral," and a third in the ventro-lateral aspect of the 



left gill i.i.M-. ( n MM M.. !i„ M , Mini is lM,th tlie larovst and most 



fuse to form wliicli pa^x- .!< .iN«.-c.'phaIa. 1 and sli.ulitlv latorail 

 until it filially fa^l.-iis to the vcntial a>iM-ct <.t' the (jor>a"l wall of 

 (he alHlonicn. After iIk- juurtini, (,f the thive l,rai,cl„-> forming 



aiul later l.y a lar.ue imi>ele haii.l from the anal re^ioi'i. Muscle 

 h, which is also a large conspicuous band of about 27 n diameter, 

 is inserted in the ventral aspect of the tissue between the left and 



