DUEING HIS SOJOURN IN THE WESTERN PACIFIC. 553 



the dorsal surface correspondingly arched. The genital pore is conspicuous on each 

 side of each proglottis. 



In examining the head of this tape-worm, soaked in oil of cloves to render it 

 transparent, it became evident that there were no hooks. The sections through the 

 head confirmed this observation. Not only are hooks absent but practically there is 

 no rostellum. A small portion — but a very small one — of the head lies in front of 

 the anterior edge of the suckers. The latter are deep and somewhat retracted in the 

 specimen and their hollow, when looked into, showed a fold or valve which has been 

 drawn in Fig. 23, Plate LV. Two suckers are dorsal and two are ventral. Each 

 sucker has a number of longitudinal muscles attached round its edge which run 

 down the neck and which contracting together would serve to withdraw the whole 

 sucker or contracting alternately would rotate it about its centre. 



Inside the head the parenchyma surrounds a nervous ganglion situated between 

 the suckers, this histological state of the material does not allow one to state more than 

 that ganglion cells and fibres are to be made out in this mass. Laterally the ganglion 

 gives off two nerves which run down the animal just external to the lateral vessels. 



The extreme anterior end of the head is occupied by a close plexus of fine 

 excretory vessels which splitting into two plexuses passed one on each side of the 

 body between the right and left suckers of each side (Fig. 23 a, Plate LVI.). These 

 plexuses consist of some 10 or 12 vessels at any one level, splitting into two and 

 running into one another. The diameter is about that of the dorsal longitudinal 

 vessel and far smaller than that of the ventral lateral vessel. Shortly behind the 

 level of the suckers, the plexuses gather themselves up into a very fine dorsal vessel 

 and a much larger ventral vessel. The latter communicates with its fellow by a trans- 

 verse vessel at the posterior end of each segment, the former gives off a number of 

 small diverticula which appear to end blindly but probably open into minuter canals. 



The most striking anatomical feature of this tape-worm is the spacious nature 

 of tlie canals of the water-vascular system. The dorsal vessel soon disappears but 

 the ventral vessel maintains a capacious cavity which communicates with its fellow 

 at the posterior border of each proglottis (Fig. 23 a, Plate LVI.). At the point of 

 emergence of the transverse vessel from the longitudinal the latter slightly contracts 

 and the entrance to the former is guarded by a valve which only permits fluid to 

 enter them when flowing from before backwai'ds (Fig. 24, Plate LVI.). The figure 

 just mentioned hardly does justice to the large space of the proglottis which is taken 

 up by the transverse vessel, and this space relatively increases as we pass from 

 before backward. Fig. 25, Plate LVI., is a transverse section, cut slightly obliquely 

 through one of the most posterior proglottides. On the right side the spacious uterus 

 containing ova is seen and on the left the still more spacious transverse commissure 

 of the water-vascular system. It will be noticed that the latter has an even greater 

 dorso-ventral width than the uterus. The same appears true of the anterior-posterior 

 diameter and the Figure 26, Plate LVI., shows that the lumen of the transverse 

 water-vascular canal is as great if not greater than that of the uterus and occupies 

 at least half the cubic content of each proglottis. I am unacquainted with any other 

 species of tape-worm which has so large an extension of its excretory-system. 



