256 Transactions of the Society. 



frequently begin in segments 4-5, and may even be found in the 

 second segment, but do not, as a rule, occur in those segments 

 which have organs of generation. The earlier views on this subject 

 are, however, somewhat modified by the fuller knowledge acquired 

 during recent years. One of the characteristics of the family as 

 hitherto known was based on the position of the reproductive 

 organs. The testes, as a rule, are found in the 11th segment and 

 the ovaries in the 12th. The girdle usually occupies the 12th 

 segment, and it is here that tlie sperm-ducts open by a reduced 

 spermiducal gland. Usually the du(;t is more or less elongated, 

 regularly or irregularly coiled, and attached to a funnel whose 

 size and form are very variable and supply admirable species- 

 characters. 



Finally the spermathecse, which are with one exception {Henlea 

 puteana) limited to a single pair, are found to open in the furrow 

 between the fourth and fifth segments, and are usually attached to 

 the intestine. These spermathecte may consist of a simple sac, 

 lying in the coelom, or a tube ; but frequently they possess an 

 ampulla, a number of diverticula, or specialized glands, all of 

 which are of value to the systematist. 



In 1895 Michaelsen recognized twelve genera. Beddard did 

 the same, but the two lists differed slightly in their components. 

 In 1900 Michaelsen {^) made out thirteen genera, and to this list 

 Bretscher {5) has since added a fourteenth, named Hydrenchij' 

 trmus. Of these fourteen genera nine have up till the present been 

 recognized as British. We are now in a position to define the 

 family, so far as the British genera hitherto known are concerned. 



11. — Definition and Scheme. 



Setse present in all genera save one (Anachseta), in four bundles 

 per segment, not forked, but straight or curved, and varying in 

 number from one in a set up to ten or a dozen. Head pore on 

 prostomium or between prostomium and first segment. Dorsal 

 pores present occasionally (especially in the genus Fridericia). 

 Dorsal blood-vessel absent from posterior, usually arising between 

 the sixth and twentieth segments, sometimes with one or more 

 heart-like processes. Blood red, yellow, or colourless. Testes in. 

 the eleventh segment and male pores on the twelfth. The girdle 

 also on segment 12 frequently extending over a part or the whole 

 of the adjacent segments. One pair of spermathecc© (except in 

 Henlea jputeana, which has two pairs), opening between segments 

 4 and 5, free within, or attached to the intestine, with or without 

 ampulla, diverticula, and glands. Salivary glands often present ; 

 nephridia of characteristic form, a pair in each segment, except the 

 most anterior and those which are occupied by organs of generation. 



