498 DR. p. soNSiNO ON DiSTOMES. [May 16, 



less than three different orders of: Mammals, undoubtedly on 

 account of the food that they may partake of in common. 



DiSTOMUM OVO-CAUDATUM, VulpiaU. 



Distomum ovo-caudatum, both of Sana esculenta and of i?. temjjo- 

 raria, has been described since 1859, by Vulpian, as living in the 

 mouths of these animals. Vulpian gave an interesting account of 

 this worm and has not failed to put in evidence the important 

 character of the presence of a basal filament in the egg, — a character 

 very rarely to be seen in the digeuetic Trematodes, but frequently 

 observed in mouogenetic or ectoparasitic Trematodes. Recently 

 Creutzburg has published an interesting study of the life-history 

 of the same worm, which according to him in its larval form is the 

 famous Cerearia cystophora, Wagener, which was once referred by 

 Willemoes-Suhm to D. lanceolatum, Mehlis. According to Creutz- 

 burg, the intermediary host of -D. ovo-caudatum, a Planorhis, would 

 become infested not by active introduction of the embryo into its 

 body, the embryo being unable to swim in water, but by eating the 

 eggs \Aith the contained embryo, which eggs are found in the faeces 

 of frogs. In a similar way the final host v\'ould be infested by 

 eating C. cystopliora contained in its nurse within the tissues of the 

 moUusk. But as yet Creutzburg has not succeeded in rearing the 

 adult worm in the mouth of a frog, by introducing the tissues 

 of Pkuwrbis containing C. cyslopliora. 



I am certainly not prepared to criticise Creutzburg's work, which 

 is only prehminary ; but I wish to point out some facts observed 

 by myself, which are not in accordance with those noticed either 

 by Creutzburg or Vulpian, respecting the worm in question. I 

 have had good opportunities to observe and study D. ovo-caudatum, 

 which I have found rather fi'equent in both Rana esculenta and 

 R. temiioraria in the neighbourhood of Pisa. I may now draw the 

 following conclusions as to the result of my observations, of 

 which I gave a full account in the ' Monitore Zoologico ' of last 

 April :— (1) D. ovo-caudatum takes up its abode not only in the 

 mouth, but also in the stomach and the upper part of the intes- 

 tines. It is perhaps more frequent in the stomach than in the 

 mouth, and it is possible that its occurrence in the mouth is merely 

 accidental, and the result of an emigration, occasioned by the 

 distressed condition of the worm on the death of the host. (2) The 

 basal filament is from 4 to 6 times as long, or even longer, than 

 the length of the body of the egg. If previous observers have 

 given a shorter length, it is probably in consequence of their 

 having seen only a truncated filament, or of not having propei'ly 

 focussed the microscope so as to see the entire length of the 

 filament, which gradually thins towards the end. (3) The embryo 

 is not only armed with a crown of spines (hdtonnets) on its anterior 

 extremity, but evidently possesses even cilia. Whether these cilia 

 aid it to swim in water when it issues from the egg, spontaneously 

 and completely mature, or are simply for locomotion in the intes- 

 tines of Planorhis, I am not prepared to say, not having seen the 



