DESCRIPTIONS OF GENERA AND SPECIES 249 



This description, 'von einer kleinen Hautfalte getragen,' suggests, as Vaillant points out (6) 

 p. 413), the parapodia of the Polychaeta. I have, however, seen in Limnodrilus a series of virart-like 

 protuberances, which bear the setae and may be the same structures. They certainly suggest 

 rudimentary parapodia; for this reason I am inclined to admit Pododrilus as a synonym, not of 

 ClitelUo, but of LimnodriluK, though the marine habit of Pododnlus suggests rather that it should 

 be included with the former genus. 



Acestus of Leidy was regarded by the author of the genus as but little different from 

 Lumhrimlus. His definition of the genus is as follows : — 



' Body vermiform. Podal spines in 4 rows ; anteriorly 3 to 8 in each fasciculus, posteriorly in 

 pairs; long sigmoid, bifurcated at extremity. Upper lip conoidal, inarticulate. AnnuH under 100. 

 Blood red. Eyes, girdle, and muscular stomach none.' 



Imperfect though this definition is, it clearly shows that Acestus is not a Lumbriculus (at least 

 auctorum; it is identical with Leidy's Lumbriculus), or a Lumbriculid of any kind known. In the 

 Lumbriculidae there are only two setae to each bundle. Its probable identity with ClitelUo or 

 Limnodrilus) was first pointed out by Czeeniavsky (p. 326), who also very justly ranged 

 Lumbriculus (Leidy nee Geube et plurimorum auctorum) under the same heading. In this he is 

 followed by Vejdovsky (24, p. 45), but not by Vaillant, who places Acestus under Lumbriculus, 

 Gkube, a proceeding which has no justification except on the view that Leidy, who was acquainted 

 with the real Lumbriculus, omitted from his definition facts which would show its identity with 

 that genus.' 



The species of the genus Limnodrilus, so far as they are known, are invariably 

 fresh water in habitat. The principal character of the genus, which distinguishes it 

 from all other Tubificidae except ClitelUo, is the presence of uncinate setae only ; 

 it is distinguished from ClitelUo by the presence of a prostate and by the great length 

 of the narrow and much-coiled vas deferens. The chitinous penis, which is longer 

 in some species than in others, distinguishes Limnodrilus from Tubifex. A character 

 which is peculiar to Limnodrilus is the presence of vascular tufts penetrating the 

 epidermis ; these are given off (in the posterior region of the body) from the peri- 

 intestinal vessels ; a branch arising from each of these loops, near the middle, dilates 

 into a sinus covered externally with pigmented cells ; from this sinus four or five 

 capillaries penetrate the integument as far as the middle of the epidermis, and then 

 appear to end blindly. 



The three European species, L. udeJcemianus, L. koffmeisteri, and L. claparedianus, 



can be readily distinguished, but it is not always so easy to make out the American 



species described by Eisen (in 7 and 12). The form of the brain and the comparative 



length of the chitinous penis sheath appear to be the most salient characters ; but, as in 



some cases, there is not an agreement between Eisen's figures and those of other authors 



(compare for example the figures of the brain of Spirosperma ferox, given by Eisen 



and Stolc respectively), a certain amount of doubt necessarily arises as to the value 



which can be legitimately attached to these characters. A revision of the genus would 



probably reduce the species considerably. 



K k 



