70 Mr. W. Nicoll on the 



of pure frcsli Mater. Some examples, l)otli from pools and 

 from (litdies, Mere eoiiHiied in a tank of I'resli water. For 

 two months they were supplied with pond-weeds, snails, 

 grubs, &e., which, however, they did not accept very readily. 

 At the end of that time some were examined and found to 

 contain the parasites as frequently as hefore. No new 

 ])arasites had ninde their appearance. For another two 

 months the sticklebacks received no food at all, and on 

 examination thereafter no diminution in the number of 

 parasites was observable, although by this time the Hsh were 

 m a very poor condition. This is at variance with the 

 observations of Zsehokke and others, who found that in fish 

 miirrating from the sea to rivers the parasites acquired during 

 their sojourn in the sea were gradually killed off by the fresh 

 water of the river. The above experiment appears to indicate 

 that the disa])pearance of the parasite s in certain cases is not 

 wholly attributable to the effect of tiie fresh water, but that 

 some other factor must enter into account. The length of 

 tmie (four months) during which the fish were confined to 

 the fresh water was ample for any effect due to the water 

 to have taken place. The only noteworthy circumstance 

 observed was the largely increased number of ova extruded 

 from the parasite in the intestine of the host. 



The following is a list of the hosts examined, with their 

 res])ective parasites ; the habitat is also noted. An asterisk 

 prefixed to the habitat denotes that the parasite is recorded 

 lor the first time from this situation ; an asterisk prefixed 

 to the name of the parasite denotes that it is here recorded 

 for the first time from this host. The fish are named 

 according to Day's 'British Fishes.' 



ACANTUOPTEIIYGII. 



Gasterostitis aculeatvs, Linn. 3-spined Stickleback. 



Podocotylo atouiou, llud. tStumacli, intestine. 

 ( = Psilostomuui reductum, milii.) 



♦Ascaris sp. (juven.). Bod^'-cavity. 

 Cottus scorpius, lilocb. Bullhead. 



Podoeotyle atomon, liud. Intestine. 



(=Di.stomuui simplex, liud.) 



Derogenes vaiicus, Miiller. Stomach and *intestinc. 



Distomum sp. Gills in capsules. 



Echinorhynclius acus, Rud. Intestine. 



Jiothriocephalus punctatus, Rud. Intestine. 

 Cottus buhalis, Euphr. Pather-lasher. 



I'odocotyle atomon, Rud. Intestine. 



•Ilemiurus appeudiculatus, Rud. Stomach. 



♦Derogene.^ varicus, Miiller, Stomach. 



*Proaorhynchus squamatus, Odhner. Intestine and pyloric 



appendages. 



