DESCRIPTIONS OF GENERA AND SPECIES 207 



some evidence of commencing disappearance ; a second stage in this disappearance 

 is, possibly, exhibited by the genus Phreodrilus, a genus of rather doubtful affinities ; 

 in this Annelid the single sperm-duct is furnished with a diverticulum which joins 

 it some way before it opens into the terminal gland. This diverticulum is, indeed, not 

 ciliated, and its epithelium is in some other particulars unlike that which line the 

 sperm-ducts ; it is more like the epithelium which lines the spermatheca of the 

 same worm, and I have suggested that we may possibly have here an indication 

 of the formation of a spermatheca out of the second sperm-duct, which would be 

 a remarkable and interesting example of a change of function. A third step is 

 seen in Alluroides, a genus which, I think, is necessarily to be referred to the 

 Lumbriculidae ; in this Annelid the sperm-ducts are a single pair only. Apart from 

 the forms that have been considered, there are no others that appear to show marked 

 intermediate characters between the Tubificidae and the Lumbriculidae ; but a con- 

 sideration of these genera leaves very few points in which the Lumbriculidae are 

 peculiar ; the only point is really the presence of a gland near to the spermathecae, 

 which has been called the Albumen gland ; this gland has not hitherto had its 

 counterpart in the family of the Tubificidae ; but quite recently a gland, which 

 appears" to me to be strictly comparable, has been described in Emholocephcdus 

 velutinvbs, a worm which, in all its other characters, must be undoubtedly referred to 

 the Tubificidae, though presenting also certain points of affinity to the Naids. 



The only other point which, in the present state of our knowledge, seems to 

 distinguish the Lumbriculidae from other worms (including the Tubificidae), is in 

 the vascular caeca. This structural peculiarity is not quite universal ; for Stylodrilus 

 has not these caecal appendages, and Vejdovsky (24) has spoken of it as a genus 

 which, in many respects, recalls the Tubificidae. There are no other points in which 

 the Lumbriculidae as a whole are to be distinguished from the Tubificidae ; no 

 LumbricuKd has capillary setae, but then these setae are occasionally wanting in the 

 Tubificidae — for instance, in the genera Clitellio and Limnodrilus ; moreover, the 

 dorsal setae of Phreodrilus seem to be intermediate between ordinary capillary setae 

 and the sigmoid setae of the Lumbriculidae. 



Family LUMBRICULIDAE 



Depihition. Aquatic Oligochaeta of moderate size. Setae paired and /-shaped, 

 sometimes with the free extremity bifid. The dorsal blood-vessel or the 



