Page:VCH Worcestershire 1.djvu/168

 A HISTORY OF WORCESTERSHIRE is still a chance that where the foe exists there also the victim may be found. Of the Branchiura the single British species, Argulus foliaceus (Linn.), parasitic on carp and trout and sticklebacks and some other fishes, is likely to be met with wherever its hosts are systematically searched for its discovery. It is easily recognized by its disk-like form and the pair of suckers which represent the second maxillas. Among parasites, which offer so rich a field for minute research, two others may be mentioned as with little doubt occurring in Wor- cestershire. These are the Copepoda, Achtheres percarum^ von Nord- mann, and hernceopoda salmonea (Linn.). They agree in having one of their pairs of jaws, the maxillipeds, modified for attachment to the body of the fish they infest. As the specific names indicate, the former species devotes itself to the perch, while the other gives a preference to the salmon. The salmon, with its change of residence from salt water to fresh, has the interesting privilege of changing its parasites, the marine Copepoda forsaking it after it has left the sea, and giving place to the freshwater Lernceopoda. But I have the authority of Mr. J. W. Willis-Bund, F.L.S., of Wick Episcopi, Worcester, for including in the fauna of the county the seafaring parasite which is found on the clean- run salmon. The creature in question is named Lepeophtheirus stromii, Baird. It is much less abnormal than the form with which it is wont to change places, but still adaptation to life on the slippery body of a fish has made it in some respects unlike the free-swimming members of its order. It has a flattened appearance, the front division broadly oval, the tail part long and narrow, but not nearly so long as the parts which are frequently supposed to be its tail, namely, the two slender ovisacs, or egg-bearing tubes, which are three or four times as long as the body. The male is much smaller than the female. Mr. Willis-Bund has also observed parasites on trout and on some of the Cyprinids. Of the latter the carp is known to entertain Ergasilus sieboldii, von Nordmann, and other members of the family support other Copepoda of various eccentric shapes. On the whole, then, it will be understood that if observed facts are rather meagre for a carcinological history of Worcestershire, there are very considerable natural opportunities for its future development. 130