ON TWO NEW GENERA OF AQUATIC OLIGOCH^TA. 281 



I believe that the reason why Eisen discovered no lateral branches of the ventral 

 cord is simply due to the fact that the worms were dissected, and not studied by 

 the section method. A dissection of Phreodrilus would certainly reveal no lateral 

 nerves, for these arise from the ventral surface of the cord, and at once become lost 

 in the subjacent body-wall. In longitudinal sections they are easy enough to see. 



Perhaps some of the other nerves of Lumbriculus escaped Vejdovsky's notice for 

 the same reason. In any case, it is noteworthy that it is in the Lumbriculidse only 

 where observers have partially (?) or entirely failed to find the lateral branches ; and 

 as in the remaining families they have been figured as projecting some way from the 

 ventral cord [cf. for Chcetogaster, Vejdovsky [7], pi. v. fig. 4, and for Dero, Stolc, 

 [6], pi. i. fig. 6], this fact is so far an indication of affinity to certain Lumbriculidse. 



As to the minute structure of the ventral nerve cord, I may mention that the 

 "neurochord" is a single tube which I traced for a considerable distance forwards. 



The connection of the neurochords in Lumbricus with the processes of nerve cells, 

 and the demonstration of their nervous nature, has been recently the subject of some 

 admirable investigations by Friedlander. I am not aware that these discoveries 

 have, as yet, been extended to the lower Oligochseta, and I may, therefore, direct 

 attention to fig. 8 of Plate I., which illustrates a branch of the neurochord passing 

 down at right angles to the axis of the chord. I have not, however, traced these 

 branches into ganglion cells, and they seem to occur at the points where nerves are 

 given off. 



§ Testes. 



The testes of Phreodrilus lie partly in segment X, but chiefly in segment XL In 

 the semidiagrammatic sketch of the genitalia (fig. 5), the testis of each side is repre- 

 sented as perforating the intersegmental septum between segments X and XL In 

 longitudinal sections I have found a perfect continuity between the portions of the testis 

 which lie in front of and behind this septum. When a section is examined that passes 

 considerably to one side of the median axis of the testis, an appearance is presented of two 

 distinct testes, such as Claparede described in Pachydrilus [1], depending into the ccelom 

 from opposite sides of the same septum. There is, however, no doubt that in Phreodrilus 

 the germinal tissue is perfectly continuous through the septum. At both extremities 

 each testis is frayed out into irregularly shaped processes, which contain the germinal 

 cells in the most advanced stage of development. The body cavity in the neighbourhood 

 of the gonad is occupied by a quantity of developing and fully developed spermatozoa. 

 I did not observe anything remarkable about the spermatozoa or their development, 

 except the important fact that all stages of this development are found in the general 

 body cavity. There was no trace of a sperm sac, which is a nearly universal structure 

 among the Oligochseta. As ripe spermatozoa were abundant in the body cavity and in 

 the circumatrial sac (see below, p. 263), I think it probable that no sperm sac other than the 

 circumatrial space is ever developed. However, as the worm possessed no recognisable 



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