188 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



namely, peculiar basal cells whose free parts project into a fibrous meshwork in the 

 spaces of which there is to be found a fluid with very fine granules, more nearly 

 approach the condition about to be described. 



In the plerocercoid described above (PI. XIX, Fig. 4) the end-organ extends 

 220fi from the apex. Its cross section throughout the series is somewhat elliptical, 

 the major axis measuring at its greatest 290/i and the minor 196/Lt, diameters 229 

 and 230/1, thus presenting a more nearly spherical outline. The organ has a thick 

 wall composed of two layers. The outer and thicker is made up of comparatively 

 large muscle-fibres running in a general circular direction and intermingled with 

 longitudinal fibres which constitute the inner layer. These fibres fuse with the 

 cuticular musculature at the anterior end of the end-organ. Next towards the 

 centre of the organ comes a very thin basal membrane much resembling the cuti- 

 cula on the exterior of the plerocercoid and continuous with that lining the in- 

 vagination chamber of the apex of the larva (PI. XX, Fig. 9) . The organ opens 

 to the exterior by an aperture 29/i in diameter and circular in shape. It is lined 

 with the cuticula from the surface of the worm, which continues down into the 

 lumen of the organ for about half its diameter as a thin-walled tube, perforated 

 freely, more especially as it nears the centre of the organ, by wide irregular open- 

 ings. This tube is supported by numerous radiating strands of tissue attached 

 to short, conial and wedge-shaped processes from the cells situated on the basement 

 membrane. In most series of plerocercoids of this age these radiating filaments 

 disappear at the posterior end of the organ as distinct connections between the 

 basal cells and the central tube, leaving only scattered pieces lying in radial direc- 

 tions from the latter. The general arrangement is best seen in transparent prep- 

 arations of whole plerocercoids; in these the strands all appear to emanate from 

 the aperture of the organ. The basal cells are very irregular, granular, highly- 

 stainable and have large nuclei, themselves readily taking the stain. The pro- 

 cesses both free and attached to the central tube are bathed in a fluid filling the 

 organ, which is very fine and granular in consistency and stains very deeply with 

 Heidenhain's iron-haematoxylin. In some series a clear area surrounding the 

 inner end of the central tube shows where some of the material has been expelhid 

 from the organ, since in longitudinal sections a band of material is often found 

 protruding through the aperture to the exterior. 



LaRue discusses this end-organ at some length in P. filaroides, among other 

 things mentioning its occurrence in the plerocercoid found in M. dolomieu, in all 

 probability that being dealt with in this paper. Apart from this species the end- 

 organ has been described only in Riggenbach's P. sp. ?, P. Lonnhergii Fuhrmann, 

 and in P. ambloplitis Leidy, the latter by Benedict. 



As to the function of the organ, if it has any definite function, the extent of 

 my studies will hot permit me to give anything further than suggestions. From 

 its early disappearance in P. filaroides and its great development in this plerocer- 

 coid, one would be inclined to conclude that it functions only in the larval stages, 

 since obviously the organ as found in the adult is functionless at least so far as the 

 external surroundings of the plerocercoid are concerned. Unfortunately I have 

 not at hand a complete series from the plerocercoid to the adult stage, the oldest 



