H. Friend l'01 



of segments 11 and 13, is taken up by the clitellum or girdle. 

 Underneath the vacuolar or glandular layer is another composed of 

 muscles arranged longitudinally, which extend throughout the entire 

 length of the body. A very thin cuticle covers the outer muscular 

 layer. The anus is terminal, and is usually very glandular. 



2. Internal characters of Henlea fragilis. 



Nervous system. The brain lies in segments 1 and 2, and in longi- 

 tudinal vertical sections is oval in outline (Plate XXXII, br.). Viewed 

 dorsally, however, the brain appears in the living worm somewhat 

 longer than broad (Plate XXIX, fig. 3), nearly or quite straight in front 

 and concave behind. At the same time it must be noted that the 

 posterior margin is liable to considerable modification, and may appear 

 to be straight or even convex in fully adult specimens. It is composed 

 of two kinds of cells, as is also the nerve cord. Two stout strands are 

 given off anteriorly, and these bend down in the front part of the 

 first segment, in the ventral portion of which they combine to form 

 the nerve in segment 2. The structure of the nerve is best seen in 

 transverse sections (Plate XXVII, fig. 1, n). The shape of the brain is 

 instructive when compared with that of Fridericia, which almost 

 invariably has decidedly convex extremities and is oval in shape as 

 well as in longitudinal section. Beddard has truly remarked that 

 " the form of the brain in these worms is often highly characteristic of 

 the genus or species." 



Coelomic corpuscles. These bodies (Lymphkorper or lymphocytes) 

 are very large and conspicuous. Their size in relation to the vacuolar 

 glands of the girdle may be seen by reference to the illustration 

 (Plate XXVII, fig. 2B), while the other figures supply opportunities for 

 comparison with other portions of the system. They agree with those 

 of Henlea moderata Welch (8), and are almost round or of a broad 

 elliptical shape. Too much stress must not be laid, as Welch seems 

 to do, on their unequal distribution in the coelom, as they move freely 

 from segment to segment, and though not usually so abundant in the 

 anterior portion of the body they nevertheless have free access to all 

 the front segments, as is shown by the way in which they stream from 

 the head pore when the animal is affected by the pressure of a cover 

 glass on the microscopic slide. The coelom itself calls for no special 

 notice. 



Alimentary system. It will be convenient under this head to discuss 



