Watson: The Genus Gyrocotyle. 409 



by sections do not indicate that it is connected with the central 

 canal-system, but rather with the peripheral non-ciliated system 

 of the lateral folds. The same is true for the dense network 

 of non-ciliated canals found in the posterior rosette. This rosette 

 region is riddled through and through with small carialsV much 

 like capillaries in size and structure of wall. No flame-cells 

 appear in this region. A ring-canal appears in the "neck," at 

 the level of the canal opening. Like the acetabular ring, this 

 appears to be immediately connected with the peripherally 

 situated canals, and through them with the deeper-lying larger 

 vessels (ant. ex. r., pi. 36, fig. 26.) 



In several specimens a dilation of one of the large longitudinal 

 canals has been found in the region of the vaginal opening, usu- 

 ally posterior to it. These dilations take the form of a thin- 

 walled sphere, into which the large canal empties, containing 

 droplets of a structureless yellow material. It is certain that 

 this "bladder" is not a constantly occurring structure. No 

 external openings have ever been found, except by Spencer 

 (1889) on G. rugosa : " Wagener was unable to find any external 

 opening of the excretory system, but, after long searching, I have 

 been able to find two unmistakable openings on the ventral sur- 

 face, one on either side of the body, slightly in front of the open- 

 ing of the uterus to the external surface." Lonnberg (1891) 

 was unable to find these openings ; the writer has never seen them. 

 But it seems highly probable that these temporary "bladders" 

 may burst through the wall of the body to form a temporary 

 external opening, closing up after the collapse of the * ' bladder, ' ' 

 due to the discharge of its contents. 



VII. NERVOUS SYSTEM. 



The nervous system of Gyrocotyle is of great interest with 

 reference to the problem of orientation, both in the genus itself 

 and in merozoic cestodes. It may be divided into central and 

 peripheral parts, according to the muscle layers with which the 

 nerve stems are related. The sense in which the phrase "central 

 nervous system" is used is of course quite distinct from the 

 meaning usually attached to it when applied elsewhere, as for 

 example to vertebrates. Neither should this use of the term be 



