1901.] OBTAINED DUKINGt THE " SKBAT EXPBDITIO]S"." 85 



the body might be vascular if the anterior end was not, since the 

 tail in the Tubificidse seems to be often used for respiratory- 

 purposes. But here, as elsewhere, I could find no evidence of 

 blood-capillaries in the skin. A specific difference in a feature 

 of such apparent importance is somewhat unexpected. But, as 

 has been, and as will be, seen, the present species is in many ways 

 divergent from its congeners. 



Male organs of generation. — As will have been gathered from the 

 account of the external features of the present species, the segments 

 occupied by the various parts of the male generative system are a 

 segment behind those which are occupied by the corresponding 

 organs in the other two species of the genus. In Bothrioneuron 

 iris the testes are in segment xi. instead of x. Excepting in their 

 position, there is nothing especially noteworthy about these gonads. 

 The male efferent apparatus, as in other species of the genus, is 

 complicated and specialised into a number of regions. In trans- 

 verse sections of the body the ventral surface was seen to be 

 flattened, and thus to contrast with the semicircular dorsal region. 

 At the sides of the body, the flattened under surface was limited 

 by a slightly projecting ridge, so that the outline of a section was 

 somewhat that of a round hat with a brim also in section. In the 

 middle of this area opens the single pore. 



When a specimen of the worm is examined in its entirety, the 

 actual orifice is seen to be small and accurately median. In longi- 

 tudinal sections the smallness of the orifice is also striking. But 

 in transverse sections it appears to be larger owing to the fact that 

 the incurving sides of the body-wall diverge from each other con- 

 siderably laterally in their course. 



The relative size of the male pore would seem to be much that 

 of B. vejdovskyanum as figured by Stole. But this author does 

 not figure microscopical sections of his species. A noteworthy 

 difference between the two species, which has already been referred 

 to in dealing with external characters, is the total absence of genital 

 setse in B. iris. In this it agrees with its nearest ally B. americanmn. 

 It is unlikely that I should have overlooked these setse in two 

 species which have been both of them examined in sections as well 

 as in their entirety mounted in glycerine. There are, in fact, no 

 seta? in the immediate vicinity of the male pore. The terminal 

 male apparatus of B. iris is divisible into the same regions as those 

 which are to be found in B. vejdovshyanum ; but their relative 

 dimensions are decidedly different, and there seem to be also 

 differences in their histological structure. The sperm-duct is divided 

 into two different sections as in B. vejdovshyanum. The proximal 

 part, that which immediately arises from the funnel, is about as 

 long as the region which follows, and is much coiled in the middle of 

 a mass of cells which represents a thickened peritoneal investment. 

 This proximal section is of less calibre, and its cells are equally 

 stained by the borax-carmine used in the preparation of the 

 sections ; the tube is also of less calibre. The remaining part of the 

 vas deferens also coils about in the midst of the cells mentioned: but 



