382 ^Ir. T. Bentham on some 



All tlie above specimens were obtainctl in the vicinitv of 

 Cullercoats, and it will be seen tliat tlie results were rather 

 ilisap)iointinjr, ten fish only bein<; infected out of tiftv-fonr 

 rxainined. This scarcity of parasites may be partly accounted 

 for b}- the fact that a great many of the fish were younp; and 

 consequently had not acquired any external ])arasitcs, and 

 also by the fact that some, as the eleven Gadus virens, had 

 been in the aqnarium for over a year, so that external para- 

 sites would have a difl^icult}' of access to them. 



External parasites were not found on any of the fish 

 except Cottus scorpius, and the three which were infected 

 with I]fomo<Tren;arines all had leeches upon them. ''J''he 

 viviparous blennies, mackerel, and skate were infected, 

 although no external parasites were present. 



It has been suggested to me that mackerel, when they are 

 not found on these coasts, possibly go far out to sea and 

 become bottom-feeders. In this stage of their life parasitic 

 leeches would have easy access to them. On tlie other hand, 

 Caligus scombri, a parasitic copepod found commonly on 

 mackerel, may possibly act as the invertebrate host. In the 

 case of the blennies the intermediate host is probably a leech 

 closely allied to CalUohdella jmncfafa, and mentioned by 

 Van Beneden in his description of that species. In the case 

 of Raia batif, the intermediate host is probably the skate- 

 leech, Pontobdella muricata. 



Technique. 



All smears of blood, spleen, liver, and gut-contents of 

 leeches were fixed in osmic acid (3 °/q sol.) to which a few 

 drops of glaci.il acetic acid had been added. They were 

 further fixed in alcohol for a quarter of an hour, and finally 

 stained with Giemsa's modification of the Romanowsky stain, 

 afterwards being differentiated with orange tannin and acetone. 

 Leishman's modification was used with good results, the 

 mixed stain and water being allowed to remain on the slide 

 for upwards of half an hour. Infusoria were examined alive, 

 and sometimes stained intra vitam with weak methylene 

 blue. Smears of Infusoria were made and allowed to dry 

 slowly in the air. Violent heating was found to dry up and 

 destroy the shape of the organisms. Staijiing with Leishman 

 was found quite effective, the cytoplasm and nuclei of the 

 cells exhibiting the usual Homanowsky reaction. 



