830 DR. F. E. BEDDARD ON A 



that the contraction of these would dilate the lumen of the dorsal 

 excretory tube. These fibres, which exist both dorsally and 

 venti-ally, have a somewhat fan-like arrangement — that is to say, 

 they converge upon the vessel from above and from below. It is 

 these various muscular layers which cause so great a variation in 

 the lumen of the excretory tube from place to place. 



The ventral vessel differs entirely from the dorsal by the entire 

 absence of any muscular layers and by the possession of only a 

 very thin lining cuticle. It follows, therefore, that the variations 

 in the calibre of this tube are not so great, and when they do 

 occur seem to be due to a squeezing by the surrounding tissues. 

 The ventral vessel also runs a much straighter course than the 

 dorsal without any marked coi'kscrew-like windings exhibited by 

 the latter. There is a transverse vessel in each segment which 

 has a i-ather peculiar relation to the ventral longitudinal tube 

 into which it opens on either side of the body. A little way before 

 reaching the dorsal tube the transverse vessel splits into two 

 halves, which embrace the dorsal vessel and open separately into 

 the ventral vessel. This is partly shown in text-fig. 115. 



We have now to deal with a series of sac-like bodies forming- 

 closed cavities of very problematical nature, which lie in the 

 middle of many segments. There is by no means one of these 

 sacs to each segment, and thus they are very far from consti- 

 tuting a tube running without intermission through the body. 

 I compare them, however, later in this paper to a tube found in 

 the young buds (see p. 833). But, as a matter of fact, one of 

 these sacs may actually extend through two proglottids, so that 

 there is a hint of a formerly continuous structui-e such as occurs 

 in the buds. As a rule, however, they appear to be limited to a 

 single proglottid, of which they occupy sometimes the exact centre, 

 at other times pushed rather to one side. They lie close to the 

 transverse water vascular vessel. I cannot find that these sacs 

 have any connection with any other spaces. They appear to be 

 perfectly isolated. The first of the series occurs very early in 

 the body — if not in the very first segment. These sacs have a 

 lining cuticle surrounded by a single layer of epithelial cells of 

 which the borders between the individual cells are not clear. 

 The nuclei, however, are very obvious and large. There are no 

 muscle-fibres at all apparent encircling the sacs. They often 

 appear crumpled in transverse sections, and occasionally seem 

 to be Y-&haped. They are impossible to miss in a series of 

 sections. 



The only remaining characteristic of this worm upon which I 

 am able to report is the structure of the " head " end of the body, 

 which has been already briefly described above. In the place of 

 a scolex there is a small projecting process, no larger than the 

 rostellar process of many vinarmed tapeworms. This arises from 

 the middle of what may be termed, for the present, the first seg- 

 ment of the body, which is distinguished from those that follow 

 by its rather less breadth and greater length. It would seem to 



