10 Transactions of the Society. 



established. The genus may, perhaps, best be distinguished by the 

 following features : — 



Setffi in four sets or bundles in each segment ; when only two 

 are present these are of equal length, but when the bundle con- 

 tains four or more tliey are more or less regularly paired, the 

 outermost being always the largest. Dorsal pores are present as 

 a rule from the 7th segment and backwards, with cells which remind 

 one of the stomata of many plants. The head-pore is usually 

 small, and as a rule is placed dorsally between the prostomium and 

 the first segment or peristomium. This is rendered by some 

 authors fractionally as 0/1. The coelomic corpuscles are of two 

 kinds— the larger being round, oval, or cigar-shaped, and often 

 with marked granulation. I'eptonephridia or salivary glands are 

 usually present. These vary much in size and character, and are 

 of great value for purposes of diagnosis and classification. They 

 lie behind the oesophagus, and extend variously through one, two, 

 or more segments. Whereas in Hcnlca the oesophagus goes sud- 

 denly into the intestine, in Fridericia it merges gradually ; and in 

 most instances the dorsal blood-vessel arises definitely behind the 

 girdle or clitellum, which is seated on the 12th segment, and fre- 

 quently extends over a part or the whole of segment 13. The 

 spermathecie are usually attached to the intestine in the 5th seg- 

 ment, and open in the intersegment 4/5 for the reception of 

 spermatozoa during copulation. Sometimes the spermathecai are 

 simple, at other times they possess two or more diverticula, and 

 these again are of high importance in diagnosis. The sperm-duct 

 near the girdle is usually long, and the nephridia have as a rule 

 a large anteseptal portion which reveals the presence of a canal. 



It will thus be seen that the species fall into series or groups 

 according to the number of the sette, the presence or absence of 

 peptonephridia, the simplicity or complexity of these organs, the 

 nature of the spermathecne, the segment in which the dorsal vessel 

 arises, and so forth. Thus m'c might have such an- arrangement as 

 the following : — 



I. Number of Setse : — 



(rroup 1. Bisetose. 

 „ 2. Quadrisetose. 

 „ 3. Multisetose. 

 II. Peptonephridia : — 



Group 1. Absent. 

 „ 2. Simple. 

 „ 3. Branched. 

 111. Spermatheca^ : — - 



Group 1. Simple. 



„ 2. Two diverticula. • 



„ 3. More than two diverticula. 



