THE ANATOMY. COELOM 29 



which VEJDOVSKY, who discovered it, compared to a lymphatic trunk ; it runs on 

 the ventral surface of the body between th > intestine and the nerve-cord, and is of 

 limited extent. 



All these tubular cavities are suggestive of lymphatic vessels. In the thickness of 

 the body-wall there are often irregular spaces and clefts which are filled with corpuscles. 

 Attention was first directed to these by KJJKENTHAL (1) who saw in them a fore- 

 shadowing of the Vertebrate lymphatic system. They occur apparently in a good many 

 different genera, but in none have they proper walls of their own ; they are merely clefts 

 and crannies left between the muscles. 



The branchiae of the genus Branchiura are hollow structures containing what 

 I presume to be an extension of the coelom. This cavity however is traversed by 

 anastomising fibres with nuclei at the nodal points ; whether it is lined by a definite 

 coelomic epithelium or not I am uncertain ; the cavity is however shut off from that 

 of the coelom by a muscular diaphragm which during life is in constant movement. 

 It seems to be quite imperforate to completely separate the coelomic and intra- 

 branchial cavities. Very frequently this diaphragm was convex towards the body- 

 cavity. If it were pulled out so as to form an ampulla lying in the body-cavity 

 there would be a state of affairs comparable to that which is met with in the cephalic 

 tentacles of Saccocirrus where MARION and BOBRETZSKY have described a cavity 

 communicating with an ampulla lying in the body and have compared to the 

 ampullae of Holothurians. 



3. Coelomic organs of problematic nature. Attached to the anterior septum of 

 segments x. and xi. in Sutroa are two bodies suggestive at first sight of sperm-sacs. 

 These are of a racemose form and are hollow ; the cavity is however not single, but 

 divided up by trabeculae into numerous subsidiary cavities. The walls are thin and 

 apparently muscular. Enclosed within the meshes are many loosely packed cells. 

 EISEN first called attention to these bodies, but compared them to the albumen glands of 

 Rhynchelmis. I could myself find no duct; and the fact that in cne case a diverticulum 

 of the spermatheca lay within the sac led me to regard the cavity of the sac as 

 coelomic. 



In certain Perichaetidae there are a series of minute paired whitish bodies lying one 

 on either side of the dorsal vessel in the middle region of the body, and springing from 

 the septa (in Pcrickaeta indica) or from the dorsal vessel itself (Perifl-irt<t <lyeri). 

 These bodies are quite solid, consisting of a mass of cells surrounding a few muscular 

 fibres. 



In Acanthodrilus fal< landicus there are a series of similar bodies commencing at about 

 segment xx. and continuing to the end of the body. They are attached to the septa near 



