Alien Oligocluvts in England. By Ecv. H. Friend. 263 



the species occupies. The problem is to ascertain the genus to 

 which it belongs, and though I have placed it for the present 

 among the Dichogasters, that is only because the more important 

 characters approach those of Diehogaster more nearly than any 

 genus whose diagnosis I have been able to study. By the w^ell- 

 kiiown process of elimination, it was possible without difficulty to 

 decide that the worm must belong to the extensive family of 

 Megascolecidte. There are four pairs of simple pointed sigmoid 

 setoe in each segment. The girdle extends over segments 13 to 20, 

 the male pore is on segment 18, and the prostates open on 

 the two adjoining segments 17 and 19. The female pore is on 

 segment 14, there are two pairs of spermathecee in 7/8 and 8/9, 

 testes and funnels in 10 and 11, and ovaries in 13, while the 

 gizzard extends from the 7th to the 10th segment. All these are 

 characters of the Megascolecidre {10). 



But this superfamily is divided into nearly half-a-score of 

 sub-families. The oesophageal glands are too far back for the 

 sub-family Ocnerodrilinae, the spermathecae too advanced for 

 Euth-ilinpe, the nephridia rule out Diplocardiinae and Acantho- 

 drilinse, and other characters make it impossible to relate the worm 

 to the Octochsetinai and the Megascolecinae. We are thus driven to 

 the sub-family Trigastrinte, and the genus Diehogaster ; but even 

 then the differences between the species now under discussion and 

 the typical Dicliogaster are considerable. 



Following the method adopted in the paper to which I have 

 already alluded, I propose to deal with the subject under the 

 headings — Historical Survey, Distribution, Description, Eelative 

 Position, and Bibliography. 



I. — Historical Survey, 



The genus Diehogaster was created by Beddard (1) in 1888, 

 in a very valuable paper on the " Structure of Uroehxta and 

 Diehogaster." Early investigators liad depended almost entirely on 

 dissection, and as a result the smallei^ forms of Annelids were far 

 from being fully and accurately described. Beddard employed the 

 method of sectionizing, and was able in consequence to extend and 

 perfect the earlier descriptions. In the case of the new type, 

 Diehogaster damonis Bedd., one worm was dissected, and the other 

 studied by means of transverse sections. The main points in the 

 original diagnosis are the following : — The setse, which are wanting 

 ventrally in segments 17, 18, and 19, are paired and occupy the 

 ventral side of the body ; the girdle extends from the 13th to the 

 20th segments inclusive, and is more fully developed dorsally than 

 ventrally. Dorsal pores present. A single pair of spermathecse 

 in segment 8 ; two gizzards, separated by a very minute ceso- 



