STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAX. I77 



matodes live attached to the gill of the fish ; l^ut many live in the 

 mouth-cavity or on the general surface of the Ijody. For instance, 

 2'ristomuni Xo:airac, the specimens of Avhich I owe to my friend Mr. 

 S. Nozawa of the Fisheries Bureau of the Hokkaido Chö, was found, 

 according to my friend's statement, attached to the fins of Tlujnmis 

 sibi. Monocotijh Ijiinae I have found parasitic in the mouth-cavity 

 of Tnjgoii pastinaca, and Dididopliora sessilis and Diclid. clongata res- 

 pectively in that of Cliarops Japonicus and Vagnis tumifrons. It is 

 stated by Monticelli'^ that some species of Octocotijlidac are parasitic 

 on Cymotlwa ; I have once found a single specimen of Dfc/ü/o/)/(ora 

 clongata attached to the caudal segment of a Cgmothoa, and according 

 to Prof. Ijima's statement in manuscript DicUdopliora smaris 

 was also found attached to a Cijmothoa. But as Prof. Ijima 

 remarks, these facts alone cannot be taken as proving that these 

 Trematodes are true parasites of the Cijmcthoa ; for all the other 

 specimens of DicUdopliora domjata which I have collected from the 

 same host were found attached directly to the wall of the mouth- 

 cavity, and therefore the single specimen that was attached to the 

 Ctjmotlioa must be regarded as accidental. It is, however, quite other- 

 wise with Tristomum hiparaHiticum. In the first place, every one of the 

 specimens of this species that I have collected was attached to the 

 carapace of a copepod, probably of the genus ParapctaUis, parasitic on 

 the gill of Tlnjiinus alhacom ; and in the second place, a very curious 

 relation exists between the Trematode and the copepod. I have 

 namely found the e^g of the former attached to the ventral side of an 

 abdominal segment of the copepod. In most specimens two eggs were 

 attached to one individual in like positions on the two sides, but in 

 some I have found only one. The Qg(g I have reproduced in fig. 4r(, 

 PI. XXV ; and as may be seen from the figure, the chitinous shell 



1). Monticelli— Saggio, p. 18. 



