002 T. IKEDA : 



the larvœ of types B and D are best suited for this purpose, as 

 the muscles in these are remarkably large and hjng. Figs. 63 a-c 

 are taken from serial sagittal sections through the right side of 

 the nerve ganglion. In figure a, a median section, we see beliind 

 the ganglion nothing 1)ut tlie preoral septum {mex\) In the next 

 figure, h, the septum is found to have shifted to a more anterior 

 position and its dorsal termination is accompanied by a strong 

 muscle-band {ret.). This band corresponds to that portion of the 

 retractor muscle which is nearest to its anterior insertion on the 

 postero-lateral side of the ganglion. The two muscles are shown 

 in fig. .39 (/ {ret.), a cross section through the posterior recess 

 (p.r.) of the preoral cavity, where they spring directly from the 

 septum (^ine^\). In fig. Go c, which shows a more lateral region 

 than fig. 63 b, the muscle is found to have retreated far backwards, 

 touching with its posterior portion the œsophageal walls {pes.). The 

 posterior insertion of the muscles on the somatic walls are best 

 studied in serial cross sections of the larva. Figs. 58 a and b show 

 two cross sections passing tlirough the mouth {a) and through the 

 middle of the œsophogus (/;). In both figures the muscles {ret.) 

 are found on l)oth sides of tlie œsophagus {(cs.). A little further 

 down they soon detacli themselves from the œsophagus and begin 

 to traverse freely the l)ody-cavity (larval collar cavity), and after 

 that thev again apply themselves to the skin on each side 1)etween 

 the first and second tentacles {f and /" in fig. 58 b). 



There is also present another pair of muscles, which can be 

 discovered only in the larvae of type C. They are so very long 

 as to equal the entire length of the trunk (fig. l^^b, ret'.). They 

 arise on each side from tlie somatic walls just above the nephri- 

 dial pore and run straight downwards traversing the trunk cavity, 

 and ending at the terminal portion of the intestine. Fig. 57 a 



