SPECIES OF THE GENUS AULODRILUS. 953 



N'ephridia. — The nephriclia are constructed on the same plan 

 as in Tuhifex. They are unpaired and lie on one side of the 

 body near the venti-al surface close to the ventral blood-vessel. 

 The nephrostome is followed by a short uncoiled tubular portion 

 with thin walls, which after piercing the intervening septum 

 undergoes several windings, before it becomes continuous with 

 the convoluted tube of the glandular mass. A small pear-shaped 

 enlargement of the tube before it passes into the glandular mass 

 is seen only in sections with some difficulty. The tube in the 

 glandular mass is coiled two or three times to form well-marked 

 loops ; it then emerges as a somewhat wider tube with thin walls, 

 on ventral side nearer the anterior end of the nephridium, and. 

 not at the posterior end as in Tuhifex. The terminal free 

 portion of the tube is short and expands near the distal end to 

 form a small vesicle, which opens to the exterior at the nephri- 

 diopore, a short distance in front of the ventral setce. The 

 first nephridium lies in the 11th or 12th segment, after which it 

 is present regularly in every segment, except in the terminal 

 portion of the body. 



Nervous system. — The cerebral ganglion is deeply cleft in front, 

 slightly so behind. The median lobe, which characterizes the 

 brain of Tibhifex and other Tubificids is here absent, but a median 

 nerve is given off anteriorly to the prostomium. The peri-pharyn- 

 geal cords unite in the 2nd segment to form the fii'st ganglion 

 of the ventral nerve cord. The giant nerve fibres so charac- 

 teristic of the nerve-cord in the Tubificidas are absent here. 



Genital organs. — I collected on several occasions between the 

 middle of February and the end of April a few specimens having 

 these organs at various stages of maturity. The genital organs 

 are placed far more anteriorly than in any other Tubificid, i. e. in 

 segments 6 and 7 ; in other Tubificidae they are never present in 

 front of the 9th segment except in Tuhifex [Ilyodrilus) hedoti, 

 where they lie in segments 8 and 9. In this respect Aidodrilus 

 kashi comes near the family Naididte, in which the sexual organs 

 lie in segments 5 and 6. The gonads are the first organs to appear 

 whan the period of sexual maturity sets in. In one specimen 

 only testes were present ; on the other hand where the sexual 

 organs were fairly advanced, the testes had entirely disappeared, 

 having given rise to an enormous ma.ss of developing sperms, 

 which filled the 6th segment and the sperm-sac. The ovaries 

 are always present till the latest stage of maturity and are quite 

 large, as in other Tubificids. 



The testes are ovoid masses, one on each side, attached by a 

 narrow base to the posterior face of septum 5/6 near the ventral 

 body- wall. 



The ovaries in a stage of advanced maturity are a pair of large 

 massive organs of a somewhat ovoid or irregular form with a 

 small basal stalk, by which they are attached to the postei'ior face 

 of septum 6/7 near the ventral pai-ietes. They remain throughout 

 the sexual phase, even when the ovisac is filled with ov;i and 



