200 Studies in Enckytrcieid Worms 



sections by the aid of Zeiss and Leitz objectives and camera lucida. 

 The worms were kept for a time in damp blotting paper before being 

 killed, in order to clear the intestine and render the making of sections 

 both safe and easy. 



1. External characters of Henlea fragilis. 



An enchytraeid worm with colourless blood, closely related to 

 Buchhohia and Bryodrilus, of normal size and appearance with an average 

 length of 12-15 mm. and possessing about 50 segments. Each segment 

 save the first and last bears setae (Borsten), but those found on segment 

 12 disappear as the adult stage is reached and the girdle begins to develop. 

 Apparently the smallest and innermost setae in the ventral bundles 

 of segment 12 are those which hold on most tenaceously, and are the last 

 to disappear: a point which may not be without significance. The setae 

 are arranged in four bundles on each segment (Plate XXVII, fig. 1) and 

 are disposed, not at equal distances around the body, but on the lateral 

 and ventral surfaces. They vary in number in different specimens and 

 at different times. The largest number yet recorded for any bundle is 

 eight, and so high a number has only been found rarely and in perfectly 

 adult forms. There may be as few as two in a set, particularly in 

 immature specimens, and the size varies as well as the number. 



The head is nearly oval in longitudinal section, showing a slight but 

 distinct depression in the middle region (Plate XXXII, dep.). Between 

 the prostomium and the first body segment the head pore (h.p.) is 

 seen. It lies in the intersegment 0/1, but is not easily found in the 

 living worm, though its presence may be readily detected by the stream 

 of coelomic corpuscles which is forced out under the pressure of the 

 cover glass. It communicates directly with the coelom, and gives 

 relief to the body contents. Its close proximity to the brain might 

 suggest that it serves specially to prevent congestion in that region. 

 There are no other pores on the dorsal side. 



Vacuolar or glandular cells occur at intervals in the body wall. They 

 are neither so large nor so numerous as those which are found on the 

 girdle, and in neither instance are they arranged in definite rows, as 

 is the case with some of the Enchytraeids. These cells are usually 

 more numerous on the dorsal than on the ventral surface. 



The clitellum is exceedingly glandular (Plate XXVII, fig. 2 A), the 

 vacuolar cells extending light round the girdle when the adult stage has 

 been perfectly attained. The whole of the 12th segment, with portions 



