DURING HIS SOJOURN IN THE WESTERN PACIFIC. 539 



Walter, who gives a much more complete account of the nervous system of 

 M. proteus, an animal better adapted for the investigation of this tissue than is 

 M. triyonocephulum, describes nerves going off from the side of the ganglia in addition 

 to the two mentioned above. I was only able to find such a nerve on the left side, 

 it soon lost itself in the outer end of the generative organs. 



There is no connective tissue sheath to the nervous system, which lies simply 

 embedded in the parenchyma. 



The Excretory System. 



The excretory pore is situated at the posterior end of the body, behind the 

 hindermost parts of any of the other systems of organs, yet it is not quite terminal 

 but rather opens on the dorsal side of the body (Fig. 8, Plate LIV.). 



The pore is median and minute, it leads into a very tine duct lined with a stout 

 cuticle, the mother-cells of which are small with large nuclei and these stand out 

 in marked contrast to the pale parenchyma which surrounds them. Passing forward 

 this median duct soon reaches the level of the terminal branches of the alimentary 

 caeca and here it enlarges into a capacious vesicle. The vesicle is posteriorly surrounded 

 by cells similar to those which encircle the duct, anteriorly however these cells are 

 absent and all tbat is to be seen in section is a clear space surrounded by a sharply 

 defined cuticle which externally abuts on the parenchyma of the body. 



Walter describes in M. proteus and in M. reticulare, ceitain ciliated grooves or 

 diverticula which form the posterior walls of the vesicle and which converge towards 

 the pore. A similar funnel-shaped opening exists in M. trigonocephalum but Walter 

 is not so clear as to the ciliation of its ftirrows and ridges. I also have seen 

 appearances which may be due to cilia badly preserved but before pronouncing an 

 opinion I should like to see them flicker in a live animal. Such a ciliated external 

 termination of the excretory system is as for as I know not described in other genera 

 of Trematodes. It may obviously help to expel the waste products and its presence 

 may be correlated with the absence or very slight development of the musculature 

 of the vesicle which is a characteristic feature of the three species mentioned above. 



About the level of the anterior third of the testes the vesicle, which by this 

 time has narrowed, splits into two main tubes which continue to run forward in the 

 same horizontal plane and at first lie parallel one to another. 



Each branch runs forward, lying on the whole below the limb of the alimentary 

 canal of its side. Anteriorly the right and left branch unite below the oesophagus. 

 About half-way along the length of the chief lateral vessel — the exact position is not 

 invariably the same in different .specimens — a secondary vessel arises which passes still 

 more ventralwards and runs in the edge of the animal to the extreme posterior limit 

 of the body (Fig. B in text). 



I could trace no smaller vessels arising from these main ones and could see 



w. V. 72 



