STUDIES ON THE ECTOPAEASITIC TREMATODES OP JAPAX. I77 



matodes live attached to the gill of the fish ; but many live in the 

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

 Tristomum Nozaivae, the specimens of which I owe to my friend Mr. 

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

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

 sibi. Monocotijle Ijimae I have found parasitic in the mouth-cavity 

 of Trygon pastinaca, and Diclidophora sessilis and Diclid. elongata res- 

 pectively in that of Chcerops Japonicus and Pagnis tumifrons. It is 

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

 on Cyviothoa ; I have once found a single specimen of Diclidopliora 

 elongata attached to the caudal segment of a Cymotlwa, and according 

 to Prof. Ijima's statement in manuscript Diclidopliara smaris 

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

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

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

 specimens of Diclidopliora elongata 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 

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

 wise with Tristomum hiiMrasiticwn. 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 Parapetaliis, parasitic on 

 the gill of Thynnus alhacora ; and in the. second place, a very curious 

 relation exists between the Trematode and the copepod. I have 

 namely found the egg 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 egg I have reproduced in fig. Aa, 

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



1). Monticelli— Saggio, p. 18. 



