130 Dr. P. de Filippi on the Larvce of the Trematode Worms. 



considerable size^ and by a very small, conical, buccal spine. 

 These Cercarise are contained in a sac or viscus with distinct 

 proper walls. 



At a later period I found in a Lymnaus pereger other similar 

 sheaths, but less lively in their movements, and with a more 

 granular tissue. They only contained germs ; so that I should 

 not mention them if they had not furnished me with an inter- 

 esting observation which may throw some light on the nature 

 of these creatures. In fact, in these sheaths, the internal sac, 

 full of germs of Cercariee, not only possessed very distinct walls, 

 but in several it presented a more or less complete constriction, 

 indicating a scission in coui'se of taking place, without any parti- 

 cipation of the external envelope forming the sheath properly so 

 called. It follows from this, that these sheaths are not simple 

 nurses or Sporocysts, but grand-nurses {Grossammen) or Sporo- 

 cystuphores, as the name of Sporocyst must be reserved for the 

 internal sac tilled with Cercarise. 



Although we are destitute of direct obsenations upon the 

 development of these Sporocystophores, it is reasonable to sup- 

 pose that in this respect also we shall find good reasons for con- 

 sidering them as a perfectly peculiar kind. In fact, the Sporo- 

 cysts are produced by the du-ect metamorphosis of an infusoriform 

 embrvo; the Rediee are procreated by a similar embiyo, which 

 soon afterwards dies and becomes decomposed. Probably the 

 Sporocystophores correspond with the primitive embryo, which, 

 after having undergone a transformation, would persist along 

 with the Sporocyst procreated by it. 



Planurbis carinatus furnished me with a second species of 

 Redia, originating directly from true Distoma, and nearly analo- 

 gous with those which I have already indicated as parasites of 

 Paiudina impura*, but which arrive, in the Redia itself, at a 

 still more advanced state of development, even presenting a ru- 

 diment of a generative system. The excretory organ, which is 

 also very different, presents the form of a small contractde ve- 

 sicle, in which the very delicate and tortuous vessels of each 

 side of the body are clearly seen to terminate. 



Lodged in the viscera of this Planorbis I also found an im- 

 mense quantity of Sporocysts producing very large, armed Cer- 

 carise, of a species not hitherto described, and distinguished at 

 the first glance by their greatly developed excretory organ, which 

 has a double outline, and is, as it were, trilobate. The ventral 

 sucking-disk is larger than the anterior one; the two lateral 



* Memoire pour servir a I'liistoire genetique des Trematodes, figs. 29- 

 31, Turin, 1854; and Annales des Sciences Naturelles, tome ii. p. 255 



(1854). 



