MYZOSTOMIDA FROM THE RED SEA. 105 



A series of transverse sections was obtained, and they 

 show a very characteristic feature of this species, namely, the 

 great development of the " Hautmuskelschlauch," the muscle- 

 sheath below the skin (PI. VII., & PI. YIII. fig. 1) ; it is best 

 developed on the dorsal side of the animal, where it is separated 

 from the outer epithelium by a cutis-like layer of connective tissue. 

 This cutis is absent from the ventral surface, and here the muscle- 

 sheath can be seen to consist of distinct outer and inner layers of 

 transverse and longitudinal fibres respectively. 



Alimentary Canal. 



The mouth leads into a muscular elongated pharynx, which, 

 when retracted, extends back in the body almost as far as the 

 level of the second pair of parapodia. The pharynx was in this 

 condition in all four specimens, and I was therefore unable to- 

 make out whether terminal papillae occur. There is no distinct 

 esophagus, the pharynx leading directly into the stomach ; this 

 part of the alimentary canal is comparatively narrow and of 

 considerable length ; slightly sacculated anteriorly, it gives off on 

 each side three intestinal trunks which arise close together at a 

 point just posterior to the level of the third pair of parapodial 

 insertions. The central of these three trunks branehes profusely 

 in the normal manner, but supplies only a small area of the body 

 with intestinal c«ca ; the anterior and posterior trunks, however, 

 continue in a straight course forwards and backwards respectively 

 to the two extremities and, keeping close to the middle line, supply 

 the rest of the body with numerous almost parallel branches given 

 off from their external sides only. This peculiar and very cha- 

 racteristic arrangement of the intestinal branches (text-fig. 23) 

 recalls that described by v. Graff in II. elongatum {!) ; it seems 

 probable that it will be found to occur in all the elongated species. 



The rectum commences a short distance behind the last pair of 

 parapodia and runs backwards as a straight narrow tube, which 

 opens on a small but conspicuous papilla (PI. VIII. fig. 1) close 

 to the posterior margin of the body. 



I could find no trace of salivary glands in connection with the 

 alimentary canal, and the peculiar glandular tissue described as 

 surrounding the anterior part of the stomach in M. costatum is 

 very poorly developed in this species. 



Reproductive Organs, 



The single specimen sectioned proved to be in an androgynous 

 condition, and both sets of organs seemed equally developed. 



Male Organs. 



The testes (PI. VII.) are embedded in the parenchyma, chiefly 

 ventral to the alimentary canal, but a certain number of follicles, 

 as in M. costatum, extend upwards between the intestinal branches 



