204 Studies in Enchytraeid Worms 



lumen is ciliated. Surrounding the whole is an outer layer which 

 shows no definite structure, but is filled with minute dark-staining 

 points (Plate XXVIII). In this species there are no chloragogen cells 

 as shown by Welch in H. urbanensis. The dorsal blood vessel may 

 be seen (Plate XXVIII, b.v.) immediately behind the diverticulum, but 

 in front of the septum which it pushes back into the coelomic cavity of 

 the 9th segment. 



The intestine commences in segment 9, and is only distinguished 

 from the oesophagus by its greater diameter (Plate XXX, int.). 



Vascular system. The blood vessels of the Enchytraeids are normally 

 few, and the arrangement is simple. There is a dorsal vessel which 

 arises either in front of the clitellum (preclitellian),. within that organ 

 (intraclitellian) or behind it (postclitellian). In all the Henleas as at 

 present defined the dorsal vessel arises immediately behind the oeso- 

 phageal glands in or near the 8th segment. In Henlea fragilis it some- 

 times appears as if it originated in the anterior portion of segment 9: 

 but sections show that it is wont to push back the septum 8/9 (Plate 

 XXXII, sep.) in front of which it commences (Plate XXX, d.b.v.). In 

 segments 8, 7, 6 there are enlargements of the vessel, that in 8 (Plate 

 XXXII, d.b.v.) being about twice as large as the one in segment 7, 

 which in its turn is of greater dimensions than the one in segment 6. 

 Each vessel contains a substance which coagulates and stains readily 

 (Plates XXVIII and XXXII, b.v.). It cannot be seen in the living 

 worm on account of its transparent nature and the absence of a 

 colouring medium. Observations made on sections of a similar character 

 taken from the red-blooded Enchytraeids, however, show that this is 

 the blood-plasm. The dorsal vessel passes forward to the head, giving 

 off three commissures on the way, dips under the brain and bifurcates, 

 so as to form the two anterior branches of the ventral vessel. The 

 disposition is normal and calls for no further description. 



Sexual characters. The sexual organs consist of ovaries and testes, 

 together with numerous accessories, such as sperm funnels and ducts, 

 penial bulbs, male and female apertures, and the storing chambers 

 or spermathecae. We begin with the latter as being the first organs 

 which meet the eye when passing from the head backwards. 



The spermathecae (Plate XXIX, fig. 1) of Henlea fragilis, of which one 

 pair exists, are situated as usual between the first and second septals in 

 the fifth segment, the opening being in the intersegment 4/5, which 

 is destitute of glands. There are no diverticula, but an ampulla is 

 found about mid-way between the two extremities. The posterior 



