726 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [8] 



Since the aquiferous vessels occupy the same relative position with 

 reference to the fossa? of the head as the grooves ou the anterior part of 

 the body, and, as is shown by sections of mature segments, with refer- 

 ence also to the lateral rows of pores and genital apertures, the fossa) 

 are proved to be lateral. The apparent shifting of the grooves from 

 the margins of the head to the lateral sides of the body already alluded 

 to is, therefore, due to a simple twisting of the body behind the head. 

 This twisting is a natural result of the flattening of the head in a plane 

 which is at right angles to the plane of flattening of the body. 



A longitudinal section through the head shows that the central part 

 resembles the entire head of such species as D. mamibriforme and D. 

 punctatum, which have rather long and slender heads. The thin edges 

 of the lobes of the head of this species, as indeed is plainly shown by 

 sections near the apex of the head, are simply the prolonged lips of 

 normal bothria. 



With regard to the musculature, the longitudinal fibers are pretty uni- 

 formly distributed through the head a little more abundant near the 

 borders and at the center. No definite arrangement into fascicles was 

 observed in the head. The transverse fibers are very fine and abun- 

 dant, and cross each other in the most intricate fashion. Towards the 

 base of the head the longitudinal muscle fibers predominate in the cen- 

 ter. Behind the head they are arranged in fascicles. In longitudinal 

 sections made a short distance back of the head these fascicles were 

 beautifully shown. They appeared as rather large isolated bundles of 

 slightly wavy longitudinal fibers. 



The vessels of the water vascular system appear to branch irregu- 

 larly through the lobes of the head, and are not collected into the prin- 

 cipal channels until toward the base of the head. Immediately behind 

 the head the cut ends of the two principal vessels are seen in section 

 as narrow oblique apertures, .016 and .OOS nim in the two diameters. 



In respect to the disposition of the reproductive organs the results of 

 my investigations thus far are not wholly satisfactory. The reproductive 

 openings proper are situated along the median line of one of the lateral 

 faces of the body and are about the middle of the length of the seg- 

 ment. The single large aperture, which, with its slightly raised border, 

 can be seen easily with an ordinary lens, is the common opening for 

 both the sexual organs of the segment. After two or three thin longi- 

 tudinal sections have been made on the side of the segment which bears 

 the reproductive opening, the vagina is brought into view lying im- 

 mediately behind the opening of the cirrus and close to it. The male 

 aperture quickly widens into the cirrus pouch. .08 to .l mm in diameter, 

 as the sections are carried towards the interior of the segment. The 

 vagina remains of uniform size, about .016 to .021 mm in diameter. The 

 cirrus pouch in transverse sections is oval. It extends to the middle 

 of the interior of the segment, that is, the pouch is equal in length to 

 about half the thickness of the segment. The cirrus was invaginated 



