A HISTORY OF NORTHAMPTONSHIRE 



which have been described as ' intermittent parasites.' Their hosts, so 

 far as at present known, are always fishes or frogs. Upon these they 

 fasten and suck their juices, to the serious detriment of tender tadpole or 

 the smaller kinds of fish. Then, when a grateful feeling of replenish- 

 ment supervenes, they relinquish their hold of the now anaemic victims, 

 and swim about with activity in freedom to get up an appetite for 

 another meal. They are classed in an order called Branchiura, which 

 contains the single family of the Argulidce. Of this the only repre- 

 sentative known in England is the Argulus foliaceus (Linn.), the discovery 

 of which in Northamptonshire is thus notified by Mr. H. F. Tomalin : — 



' Occurrence of the Argulus foliaceus upon the common " trout," 

 Sal mo far 10. 



'The trout was caught at Holdenby in June of this year [1883], 

 and thirteen of these parasites were obtained from it ; they were how- 

 ever near to the abdominal fins, and not fixed just under the pectoral fins 

 as is more common. The occurrence of this parasite upon the trout is 

 very unusual. Thompson, in his Natural History of Ireland, records it as 

 having been obtained from this fish, and it has more recently been 

 recorded in The Field.' After an account of the classification, Mr. 

 Tomalin continues : ' The fish-argulus may be found on various fresh- 

 water fish, the two species of sticklebacks being the more general ; they 

 swim gracefully, and have a strong resemblance to the seeds of plants. 

 The female is larger than the male, and is distinguished by the black spot 

 on each side of the abdomen ; the width is about two lines. They 

 occasionally leave the fish, but not for a long time.'^ 



Mr. Beeby Thompson, in a letter already quoted, alluding to Mr. 

 Tomalin's capture, says : ' The same species, I think, I have had on gold- 

 fish in my aquarium — possibly introduced by sticklebacks.' Since gold- 

 fish are of the carp tribe, the Argulus foliaceus, which both in England 

 and Germany is often called the carp-louse, would find itself at home 

 upon them. As measurement by lines or twelfths of an inch has gone 

 out of fashion, it may be well to observe that a width of two lines is 

 equivalent to a little over four millimetres, and that the width was 

 mentioned by Mr. Tomalin, rather than the length, probably because these 

 little greenish semi-transparent vampires are disc-like in shape, and not to 

 any striking extent longer than broad. A very remarkable feature in their 

 organization is the transmutation of their second maxillae into a pair of 

 circular suckers. In this respect they differ from the species of the 

 companion genus Dolops, in which these maxillae end in strong hooks 

 instead of suckers. The Argulida were at one time arranged with the 

 parasitic Copepoda, as in Mr. Tomalin's notice, and to some of the so- 

 called fish-lice of that group they show a marked superficial resemblance. 

 But a different classification is now accepted. Even Claus, the dis- 

 tinguished German zoologist lately deceased, who argued for their 

 removal from the Branchiopoda, does not venture to include them among 

 the genuine Copepoda. In regard to their habits he is not quite at one 



' Jourti. Northampton Nat. Hist. Soc, vol. ii. p. 292 (1882-83). 



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