Dr. P. de Filippi on the Larvce of the Trematude Worms. 131 



ducts which terminate at the spine originate from a veiy pretty 

 bunch of secretory cells. This characteristic apparatus of the 

 armed Cercari;e is not so well develoj)ed in any other species. 



Amongst the Cercarire which I have already made known in 

 my previous works, and which I have again frecpicntly seen in 

 the course of this year, 1 shall mention particularly the Cercaria 

 virgnla, of which 1 have indicated the analogy with the C. micro- 

 cotylu, parasitic on Puludina vivipara^\ 1 must now add, that 

 in the form and dimensions of its Sporoeysts, the C. virgula 

 presents the same differences that I have found in the other 

 allied species. 



In some individuals of P. impura, the Sporoeysts of C. virgula 

 are large and elongated, and contain a considerable number of 

 Cercaria3 ; in others, on the contrary, we only find small Sporo- 

 eysts, usually of a rounded form, upon which we can see a sort 

 of more or less apparent umbilicus, and which only contain a 

 very small number of Cerearipe (3-4). These CerearicC are ex- 

 actly identical, both in form and organization, with those pro- 

 duced by the large Sporoeysts ; but their dimensions are much 

 less, being reduced nearly to half. On examining a great many 

 of these little Sporoeysts, we soon see that they are the result 

 of a scission of other larger ones; so that what I have just 

 called an umbilicus really merits that name, because it corre- 

 sponds with the spot at which the separation has taken place. 

 The same difference between large and small Sporoeysts exists 

 in the C microcotyla of Paludina vivipa?'a, as I have pointed 

 out elsewheref, and this difference now receives its explanation. 

 It is not impossible that these small Sporoeysts and Cercarise 

 belong to different species from the analogous large Sporoeysts 

 and Cercarise. 



I have been struck this summer by the frequency (although 

 the individuals were always few in number) of a Cercaria, which 

 was first indicated by M. de la Valette under the name of C. 

 cristataX, and which never occurred to me in my previous re- 

 searches. This singular creature, which I have met with in 

 different species of Mollusea ( Valvata piscinalis, Paludiria im- 

 pura, Planar bis submarginatus, Lymnceus stagnalis, L. palustris), 

 is still the subject of a problem with me. If it be really a Cer- 

 caria, it can only be referred to a Monostomum. 



In the month of August I passed a few days on the shore of 

 the Mediterranean, with the view of making some investigations 



* Second Memoire pour servir a Thistoire genetique des Trematodes, 

 p. 6. Turin, 1855. 



t Memoire, &c., p. 9. figs. 5, 6 (1854). 



X Symbolae ad Trematodum evolutionis historiara. Berlin, 1851. 



9* 



