SEXUAL PHASE TN IXUTA?^ NATDID.^:. 4G5 



is somewhat lieai't-shujied, ur ovoid ;ui(l iiok-lied helow where the 

 duct ni'ises. Its size varies somewhat : in heii^ht it may be from 

 207 to 270/./, its length antero-posteriorly ratlier greater and its 

 width rather less. The ampulhe are filled with spermntozoa, and 

 are so lai'ge as neai'ly to fill up the Avl.iole segment, the remaining 

 organs occupying only a small space below their contiguous inner 

 walls. The part of the ampulla anterior to the duct is somewhat 

 bulged downwards, and is lined with columnar cells ; the part of 

 the wall behind the duct is lined with cubical cells, which 

 gradually decrease in height tis they pass upwards on the posterior 

 wall ; the rest of the ampulla is lined by a very thin epithelium 

 of attenuated cells whose outline is quite indistinct. Outside 

 the epithelium there is a thin coat of circular muscular fibres — 

 the only part of the wall visible over a large portion, on account 

 of the thinness of the epithelium. The spermathecal duct leaves 

 the ampulla below, nearer its anterior wall, and is about 130-140 /j. 

 in height, including the depression of the body-wall wliere it 

 opens to the exterior. The duct is narrow above and below, but 

 so]newhat swollen in the middle ; its epithelium consists of 

 narrow columnai' cells having elongated nuclei. There is a thick 

 covering of muscle-fibres outside the eiDithelium. The sper- 

 mathecal opening lies internal to and at the level of the ventral 

 setfv of the fifth segment, some distance behind septum 4/5. 



The penial setse are the modified ventral seta? of segment vi. 

 They are tAvo or three in a bundle, somewhat hooked at the 

 distal end, which is not bifid. In length they are about 132 ix ; 

 the shaft consists of a distal narrow poi^tion about 36 ju long, and 

 a proximal stouter part 96 /j long ; there is no distinct nodulns, 

 but the distal narrow portion is bent outwards and thus not in a 

 straight line with the pi*oximal segment (text-fig. 1). 



References to Literature. 



1. Eeddard, F. E. — " A New Branchiate Oligochjete {Branchiura 



sowerhyi)." Quart. Journ. Micr. Sci. vol. xxxiii., 1892. 



2. Stephenson, J. — "On Branchiura sowerhyi Beddard, and on 



a new Species of Limnodrilus with distinctive characters." 

 Trans. Roy. Soc. Edin. vol. xlviii. pt. 2, 1912. 



3. Stephenson, J. — '-On the Sexual Phase in certain of the 



Naididae." Ihid. vol. li. pt. 4, 1915. 



4. Stephenson, J. — "On Hcemonais laurentii, sp. n., a represent- 



ative of a little-known Genus of Naididae." Ibid. vol. li. 

 pt. 4, 1915. 



