SEGMENTAL TUBES. 485 



a portion of the Wolffian body with three complete segments 

 and part of a fourth. If one of these be selected, it will be seen 

 to commence with (i) a segmental opening, somewhat oval in . 

 form (st. o) and leading directly into (2) a narrow tube, the seg- 

 mental tube, which takes a more or less oblique course back- 

 wards, and, passing superficially to the Wolffian duct (w.d], 

 opens into (3) a Malpighian body (/. mg) at the anterior ex- 

 tremity of an isolated coil of glandular tubuli. This coil forms 

 the fourth section of each segment, and starts from the Mal- 

 pighian body. It consists of a considerable number of rather 

 definite convolutions, and after uniting with tubuli from one or 

 two (according to size of the segment) accessory Malpighian 

 bodies (a. mg), smaller than the one into which the segmental 

 tube falls, eventually opens by a (5) narrowish tube into the 

 Wolffian duct at the posterior end of the segment. Each seg- 

 ment is completely isolated (except for certain rudimentary 

 structures to be alluded to shortly) from the adjoining ones, and 

 never has more than one segmental tube and one communication 

 with the Wolffian duct. 



The number and general arrangement of the segmental 

 tubes have already been spoken of. Their openings into the 

 body-cavity are. in Scyllium, very small, much more so than in 

 the majority of Elasmobranchs. The general appearance of a 

 segmental tube and its opening is somewhat that of a spoon, in 

 which the handle represents the segmental tube, and the bowl 

 the segmental opening. Usually amongst Elasmobranchs the 

 openings and tubes are ciliated, but I have not determined 

 whether this is the case in Scy. canicula, and Semper does not 

 speak definitely on this point. From the segmental openings 

 proceed the segmental tubes, which in the front segments have 

 nearly a transverse direction, but in the posterior ones are 

 directed more and more obliquely backwards. This statement 

 applies to both sexes, but the obliquity is greater in the female 

 than in the male. 



As has been said, each segmental tube normally opens into a 

 Malpighian body, from which again there proceeds the tubulus, 

 the convolutions of which form the main mass of each segment. 

 This feature can be easily seen in the case of the Malpighian 

 bodies of the anterior part of the Wolffian gland in young 



