AN ATTEMPT TO CLASSIFY EARTHWORMS. 205 



The glandular modification of the epidermis indicated by the 

 word '^cl it ell urn" is in many cases equally developed all 

 round the body, as in Perichseta ; this is indicated by using 

 the word " cingulum/' or speaking of the clitellum as 

 "complete." In Lumbricus and many others the glan- 

 dular modification does not extend across the ventral sur- 

 face : this is a true " clitellum " in the strict sense of the 

 word, or an " incomplete clitellum " using the word in its 

 wider sense. 



Intermediate conditions are sometimes met with, where, as 

 in Acanthodrilus, the clitellum is "complete'^ in the an- 

 terior part of its extent, and " incomplete '' over the last 

 two or more somites. The lower edge of the incomplete 

 clitellum is sometimes, as in Lumbricus and Rhinodri- 

 lus, further modified, presenting the appearance of a linear 

 band, or group of glands over more or fewer somites. To 

 these the name '^tubercula pubertatis" has been applied 

 by Eisen. 



The external openings of the sperm-ducts are the '' male or 

 spermiducal pores;" those of the oviducts, "oviducal 

 pores;" those of the spermathecse, the " spermathecal 

 pores.''^ The first of these is frequently placed on a more or less 

 prominent papilla, and in many worms other papillae, median or 

 paired, are present in their neighbourhood. These '' copu- 

 latory papillae" are probably of value for the diagnosis of 

 species; but it is only recently that exact observations 

 have been recorded as to the number and position of these 

 papillae in dififerent worms, and as they appear to be fully 

 developed only at the breeding season they are not of 

 value for absolute identification. Of this nature are the 

 depressed reddish papillae in Somite xxvi in the common 

 earthworm. 



The setae in certain somites are not unfrequently modified 

 for the purpose of copulation : those in more or less imme- 

 diate relation to the male pores are known as "penial 

 setae " (Lankester) ; whilst those which are found, for instance, 

 in Acanthodrilus layardus and other species, in connec- 



