140 



in the ciliated embryo of many Trematods the existence of 

 vessels representing the urinary apparatus of the Trematoda 

 and Cestoida. I could find no trace of these vessels in the 

 embryo of the Nematobothrium; and I have not been able 

 in consequence to verify the relation which Claparede^ has 

 pointed out between the calcareous corpuscles and the origin 

 of the urinary apparatus of Trematods. 



Affinities. — As we have said, M. P. J. Van Beneden, rely- 

 ing on certain anatomical characters, has assimilated Nemato- 

 bothrium to the Trematods, remarking, however, that certain 

 facts would tend to make one consider it as forming a 

 veritable transition between Nematods and Cestoids. 



The embryonic form of Nematobothrium has nothing in 

 common with that of the Nematods ; and the knowledge of 

 the embryo enables us to affirm that Nematobothrium does 

 not belong to this group of Worms. 



The embryo of all the Cestoids is characterized by a 

 common form; at the moment of exit from the eg^ it is 

 i:)rovided with six booklets : of which two are directed an- 

 teriorly, two to the right, and two to the left. There are 

 only some Cestoids peculiar to marine fishes, which, in place 

 of three pairs of hooks, present but two. The embryonic 

 form of the animal which occupies us diverges considerably 

 from that of the Cestoids ; and in spite of a certain resem- 

 blance in the form of some booklets, we do not hesitate to 

 declare that Nematobothrium is not a Cestoid. 



According to the manner of their development the Tre- 

 matods are divided into two great groujis : 1st, that of the 

 Trematoda monogenetica, comprising all the ectoparasitic 

 Trematods and some endoparasitic Trematods, such as the 

 Polystomum integer rimum of the frog ; 2nd, that of the 

 Trematoda digenetica, which presents all the phenomena of 

 ' alternations of generations.' The first have, when born, the 

 form of the adult, the second come into the world in a form 

 which gives no indication of that of the sexual animal. The 

 embryo of the Digenetic Trematods is generally ciliated at 

 the moment of birth. However, Von Siebold observed that 

 the embryo of Distoma tereticoUe is deprived of vibratile 

 cilia ; and some time after G. Wagener observed the same 

 fact in the embryo of Monostoma filum? The learned hel- 

 minthologist pointed out at the same time the existence, 

 around the cephalic extremity of the embryo, of a crown of 



• Claparede, ' Ueber die Kalkkorpersclien dcr Trematodeu : Zeitscbr. fiir 

 wiss. Zoologie,' Bd, ix. 



^ 'Mullcr's Arcliiv,' 1S54, page 16, pi. ii. Note of Wagner in a com- 

 munication by Lieberkiihn, " On the Psorospermia." 



