ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 723 



phrodite species. The fertility is probably as great as in the average bi- 

 sexual species. The formation of spermatozoa is not confined to the 

 anterior end of the gonad as in other species, but may occur in any part 

 and at any time throughout maturity. Frequently a number of sterile 

 eggs were laid at the beginning of maturity owing to the retarded pro- 

 duction of the spermatozoa. No males have been observed in this species, 

 so that they are either excessively rare or are extinct. Thus R. gurneyi 

 represents a more complete type of hermaphroditism than has hitherto 

 been recorded in the free-living Nematodes. Self-fertilization occurred 

 as the exclusive means of propagation throughout forty-six generations 

 of DipJogaster maupasi without any deterioration in the character of the 

 stock. 



Platyh.eTminth.es . 



Adult of Pearl-inducing Worm.*— T. Southwell submits a number 

 of observations which go to show (though not as yet conclusively) that 

 the pearl-inducing parasite in Ceylon oysters has only two hosts — namely, 

 the oyster and most Elasmobranch fishes, and that the adult is Tetra- 

 rhynchus unionif actor, as previously determined by Herclman. It remains 

 to prove this conclusively, and to discover how the infection of the oyster 

 is brought about. 



Endogenous Multiplication in Larvse of Tetrarhynchus unioni- 

 factor. | — T. Southwell has observed the endogenous formation of 

 larvse within the cysts in the tissue of the oyster. In each case the 

 " endogen " produced was single (a " monogen "), and was formed about 

 the centre of the parent cyst. In one case the larva was liberated from 

 the parent cyst by rupture of the wall while the cyst was lying free on 

 the slide enveloped in the blood of the host. The asexual multiplication 

 may explain why the infection of the more or less adult oyster is usually 

 extensive, although the primary infection may be inconsiderable. 



Regeneration in NemerteansJ — M. Oxner has studied the regenera- 

 tive processes in Linens ruber and L. lacteus. If a cut be made between 

 cerebral organs and stomach-intestine, the head regenerates the whole 

 posterior body. The intestine is regenerated from the rhynchoccelom, 

 which is quite different devolopmentally. 



If a transverse cut be made a little in front of the mouth, and a 

 little in front of the end of the stomach-intestine, the mid-gut is per- 

 fectly regrown in 25 to 30 days, but even after 5 months there is no 

 regeneration of the cerebral ganglia or cerebral organs or proboscis. If 

 the mouth be also removed, it is not regrown, and the gut ends blindly 

 in front. 



If a cut be made immediately behind the cerebral organs, and 

 another immediately in front of the beginning of the stomach-intestine, 

 a fragment 2-3 mm. in length is obtained without any part of the 

 central nervous system or digestive tube. It has some parts of the 

 excretory tubes, and a piece of rhynchoccelom surrounded by parenchyma 



* Ceylon Marine Biol. Rep., iv. (1910) pp. 169-72 (9 figs.). 



t Tom. cit., pp. 173-4 (2 figs.). 



% Comptes Rendus, cl. (1910) pp. 1618-20. 



