DESCRIPTIONS OF GENERA AND SPECIES 239 



that the oviduct was as described by d'Udekem and Clapaeede, Vejdovsky pointed out that 

 it was difficult to understand the fixation of the penis; nor was he able to see the complicated 

 layers round the penis, which were regarded by the authorities mentioned as representing the oviduct. 

 EiSEN (12), indeed, who accepted the views in question, still further increased the complexity of 

 the subject by distinguishing between Tubificids with a single and Tubificids with a double oviduct ; 

 later, Eisen abandoned the distinction between the two kinds of oviducts, having discovered ' a minute 

 penis-sheath ' in Telmatodrilus, which was the only representative of the former class. Lankesteb 

 threw doubts upon the interpretation of a part of the penis as an oviduct ; and (also previously 

 to the publication of Vejdovsky's great work) did Nasse. The latter asked, as did Vejdovsky, as 

 to the whereabouts of the attachment of the penis to the body-wall, if it was invaginated in the 

 oviduct ; he also considered that the end of the oviduct and the commencement of the penis were not 

 clearly indicated by this way of supposing the oviducts to be outside the penis. Dieffenbach has 

 devoted three or four pages of his studies upon the Limicolous Oligochaeta to a consideration of this 

 question ; he believed that ' most zoologists who have dealt with this question have been led along 

 a wrong path by an incorrect observation of d'Udekem"s.' Some of Dieffenbach's criticisms are 

 reallj- beside the point ; he asks, for example, how it is that the ripe ova which lie in the sixteenth and 

 seventeenth segments can press their way forwards to the eleventh ; they must get nearly as far, in any 

 case, for the true oviducts are between segments xi/xii. Their large size, too, would be as great an 

 obstacle to their passage out by the real oviducts as by the supposed oviducts ; Dieffbnbaoh thought 

 that the exit of the ova was by a partial tearing of the skin, an occurrence which he observed more than 

 once ; Vejdovsky, by treating the living worms, which were kept under observation the whole time 

 with chemical reagents, noticed the ova to pass out between segments xi/xii ; he is entitled, therefore, 

 to the credit of having first discovered that the supposed oviduct of d'Udekem, CliAPABiDE, and 

 Eisen, performed no such function, but that the ova escaped from the body by the position just 

 mentioned. 



The form of the brain varies considerably in different genera of Tubificidae, and 

 appears to be always complicated. The most distinctive feature is, perhaps, the 

 anterior median process which is sometimes (as in the genus Ilyodrilus) a mass of 

 cells continuous with the brain, and sometimes (as in Bothrioveuron) consists of 

 a median nerve communicating with a small ganglion placed a little way in front 

 of the brain (to be compared perhaps with the buccal ganglia of the MoUusca). 



The circulatory system, which has been principally investigated by Stolo (3), is 

 more complicated than in either the Lumbriculidae or the Naidomorpha. In many 

 features it recalls the cii'culatory system of earthworms. The dorsal vessel is 

 contractile, and runs from end to end of the body, on the dorsa;l side of the 

 alimentary tract. Branchiura is the sole exception to this rule, and a very curious 

 exception; the dorsal vessel in this worm is only dorsal in position as far back 

 as about the tenth segment, from this point to the posterior extremity, it lies 

 below the intestine, side by side with, the ventral vessel. Anteriorly the dorsal 

 vessel lies well above the oesophagus; in the intestinal region it is covered by the 

 peritoneum of the intestine. Besides the dorsal vessel a good many Tubificidae 

 have a supraintestinal vessel which has precisely the relations of the corresponding 



