A HISTORY OF KENT 



It should be understood that the scuta and terga are two pairs of valves 

 forming the operculum or lid of a Balanus ; the radii are the modified 

 sides of the shell's immovable compartments ; they overlap the alae 

 which are also lateral protuberances of the walls but are overlapped 

 instead of overlapping. 



Of the strange parasitic Thyrostraca it is quite clear that at least 

 one species has been found abundantly in Kent. This follows from the 

 remarks appended by Bell to his account of the crab Portunus marmoreus^ 

 which he personally appears to have procured only in this county. He 

 says, ' There is another fact relative to this species which is worth 

 recording, and that is, the extent to which they are infested with a 

 remarkable parasite, occupying the space between the folded abdomen 

 and the sternum, and having the prima facie appearance of a bag of 

 immature eggs. Both males and females are equally obnoxious to it, 

 and from its size and situation it must present an insuperable barrier to 

 impregnation. It consists principally of a mass of minute eggs, which 

 are arranged in bundles attached to filaments, like bunches of grapes ; 

 the alimentary canal passes directly through the body, the mouth being 

 attached to the intestine of the crab, which it pierces near its extremity, 

 and from which in all probability it derives its nourishment. The anal 

 opening, which is distinct and obvious, is visible without removing the 

 parasite from its position. The whole is of a rounded trihedral form, 

 and is covered by a tough but thin integument. I have occasionally 

 found it infesting Carcinus maenas, but never in such numbers as in the 

 present species.' ' It is difficult to understand how Bell could have 

 written this account without calling to mind that the parasite which he 

 had observed on the common shore crab had been already described by 

 J. Vaughan Thompson in 1836 as Sacculina carcini. There is now a 

 considerable literature concerned with the structure and life history of 

 the Sacculinidae. It cannot be taken for granted from superficial 

 resemblance that these parasites when found on different hosts belong to 

 one and the same species. 



The foregoing catalogue of Kentish Crustacea may be deemed a 

 fairly long one and well diversified. It is so. Nevertheless the natural- 

 ist will easily understand that in every direction some, and in many 

 directions very large, amplification of it may be predicted as the result 

 of future researches. 



» British Stalk-eyei Crustacea, Io8. 



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