ON THE ANATOMY OF HISTRIOP.DELLA HOMARI. 31] 



- It will be seen that there is some difference between the 

 arrangement of the main muscles in Histriobdella as com- 

 pared with Stratiodri lus. In the neck region I cannot 

 find the complicated crossing of fibres shown by Haswell in 

 his fig. 1. Nor in the posterior legs can I distinguish some 

 of the fibres he I'epresents. The muscular system of Stratio- 

 driliis is much better developed, and the presence of cirri 

 and the reti'actile condition of the anterior feet give it a more 

 elaborate muscular system than that of Histriobdella. 



c. Oblique Muscles. 



If we examine a number of transverse sections we will see 

 the body-cavity traversed occasionally by oblique strands 

 (figs. 39, 40, 41, 43, and 44). Foettinger mentions their 

 resemblance to the oblique muscles of Protodrilus, but he 

 was somewhat uncertain as to their nature. He says, " Je 

 n'ai pu m'assurer si elles etaient de nature musculaire ^' 

 (p. 457). They divide the body-cavity, as in the Archi- 

 annelids,into a circular portion surrounding the gut and a right 

 and left lateral chamber. In some of my sections they form 

 almost a continual sheet of fibres, and they are much better 

 developed than one might suppose from Foettinger's remark. 

 They are found as irregular bundles crossing the body- 

 cavity from the head to the tail region. They are well marked 

 in the posterior part of the head ; commencing at a point on 

 a line with the chitinous jaws, they are continued back into 

 the neck region in an unbi'oken succession. In the middle of 

 the segment they almost disappear, while they are more 

 prominent in the intersegmental i*egions. • In the anterior 

 and posterior parts of the generative segment they are also 

 present, but are entirely missing from the middle in the male, 

 being interrupted by the muscles and accessory glands of the 

 penis. Anteriorly they divide the testis in two portions, 

 forming a right and left chamber (fig. 39). In the anterior 

 part of the first segment they are shown in fig. 43. Here, 

 during part of their course, they touch the wall of the gut. 



