VERMES. 61 



in Aphrodite it is yellow, in a few it is colourless. It is contained 

 in two long tubes, one dorsal, the other ventral. The presence 

 of corpuscles is disputed. 



The head is generally provided with two or four tentacles. 

 The mouth contains one or more pairs of jaws (or teeth) ; and 

 the pharynx forms a protrusible proboscis. Eyes are sometimes 

 present. In Alciope there is a retina, iris, and lens. 



A few species are commensals; but they are mostly free, 

 moving about at the bottom of the sea, or living in the sand, as 

 the common lob- worm (Arenicola piscatorum}. Apparently they 

 are capable of living a long time without food ; M c lntosh records 

 a Eunice norvegica kept for three years without nourishment of 

 any kind. Eunice gigantea attains a length of four feet. Several 

 species are phosphorescent. " Tracks and burrows of Annelids 

 are found commonly in rocks of all ages from the Cambrian 

 period upwards." 



Tomopterus, forming the order Gymnocopa of G-rube, is a 

 degraded form, with no trace of branchiae or of a blood-system. 

 Although three or four inches long, it is so transparent as to be 

 nearly invisible, except in certain shades of light. In the female 

 the ova are in the general cavity of the body, there being no 

 proper ovarium. Polygordius is a transitional form towards 

 Trematoda : Schmarda places it as a pendant to Chastopoda. Of 

 its two species, P. purpureus is hermaphrodite, while P. luteus is 

 dioecious. 



The following list of families and genera is compiled princi- 

 pally after Schmarda, except that Polyophthalmus, Clymenidae, 

 and Chsetopteridae are placed by him in Oligochaeta: these 

 families are placed by Glaus in this order, which, for him, also 

 includes Sedentaria; he has, however, referred the first nine 

 families in the list below to the same group (Cephalo- 

 branchia). 



Capitellidce. Arenocolidce. Ariciidts. 



Capitella=Lumbri- Arenicola (Lob- Aricia. 



conais. worm). Ephesia. 



Notomastus. Eumenia. Aonis. 

 Dasybranchus. 



