lander: anatomy of hemiurus crenatus. 21 



is largely occupied by a mass of slightly staining granular substance, in 

 which are always found several large nucleus-like bodies. These bodies 

 are spherical or oval, and each shows a deeply staining spot near its 

 centre. They are of various sizes, their diameters varying from oA/x to 

 9 fx. In some receptacles there are present large irregular particles which 

 stain more deeply than the more finely granular substance in which they 

 are imbedded. There are usually several more or less irregular vacuolar 

 spaces in this substance, in which are often found numbers of spermato- 

 zoa and occasionally also yolk granules. I find, as did Juel, that the 

 fundus of the inner vesicle is provided with a small opening (F"'ig. 38), 

 which may communicate with one of these spaces or may simply be in 

 contact with the granular substance. No Laurer's canal is present. 



The seminal receptacle agrees very closely with that of Apoblema 

 excisum as described by Juel, except that in neither of the walls are 

 nuclei either described or figured by him. He interprets the granular 

 substance between the walls, with its included nucleus-like bodies, as a 

 Plasmodium, and appears to regard the receptacle as exhibiting a rather 

 primitive state because of its resemblance in structure to the conditions 

 that have been described iu the developing organ of other forms, where 

 it is to a certain extent a solid body. I believe, as suggested by Looss 

 ('94), that the granular substance consists in great part of disintegrating 

 spermatozoa, and also that more or less of it arises from the disintegra- 

 tion of ova and yolk celH. The nucleus-like bodies found in the granular 

 substance I believe to be the nuclei of ova. It is true that they are 

 usually somewhat larger than the nuclei of the ovarian ova ; but I think 

 the increase in size is probably due, in great part at least, to the begin- 

 ning of a process of disintegration. There often appears to be a small 

 space surrounding the nucleolus. The irregular, deeply staining frag- 

 ments are probably portions of yolk cells or of the cytoplasm of ova. 



According to Looss ('94, p. 224) the seminal receptacle is a vesicle for 

 the accumulation of unused spermatozoa and occasionally ova and yolk 

 cells, which, when a Laurer's canal is present, are ultimately discharged 

 through the canal to the exterior. In forms which do not have a Laurer's 

 canal the elements accumulate, and, as there is no way of escape, ulti- 

 mately undergo degeneration. This view explains the great size which 

 the receptacle sometimes attains in forms which lack a Laurer's canal, 

 and also the condition of the contents of the receptacle in such forms. 



The structure which is the most difficult of explanation in connection 

 with the seminal receptacle of appendiculate trematodes is the inner 

 vesicle. So far as I can see, the only method by which such a structure 



