480 PARASITES OF ANIMALS 



in Chimara monstrosa," ' Miill. Arch./ 1852. Idem, ' Beitrage 

 zur Entw.-Gesch. der Eingeweidewurmer (Preisschrift)/ 1857. 

 Wedl, " On Gyrodactylus " (see reference to my paper on ' G. 

 elegans '), ' Quart. Journ. Micr. Sci./ 1862 ; trans, from his 

 ' Anhang/ " Ueber die Gattung Gyrod./' to ' Anat. Beobach- 

 tungen ueber Trematoden/ Wien, 1858. Idem, ' Haematozoa in 

 Fishes/ &c. (1. c., Bibl. No. 58). Wigham, P., "Note on 

 Holostotnum cuticola from Roach and Bream/' 'Ann. Nat. 

 Hist./ p. 235, 1851. Wilson, W. W., "On a Parasitic Worm 

 infesting a Marine Fish (Crenilabrus rupestris)," in f Science 

 Gossip/ Jan., 1876. Yarrell, W., "Note on Tristoma coccineum," 

 in his work on ' Brit. Fishes/ vol. ii, p. 353, 1836. 



PART IV (EVERTEBRATA) . 



Since a large proportion of all those helminths that require 

 a change of hosts must needs pass into the bodies of insects, 

 crustaceans, mollusks, or other evertebrated animals, it is 

 evident that these lower creatures are almost as liable to be 

 infested by parasites as the vertebrates themselves. As a rule, 

 no doubt, the parasitic forms infesting individual evertebrated 

 hosts are not numerous; nevertheless the water-snails form a 

 noteworthy exception. Thus, some ten different species of 

 parasite are found either in or upon the common Planorbis 

 corneus ; whilst Lymnaus stagnalis, Paludina vivipara, and 

 P. impura, each support at least a dozen species. Of course, 

 the parasites are not sexually mature, since nearly all of them 

 are Cercarics or larval trematodes. Snails, oysters, mussels, 

 whelks, and other mollusks afford harbour and anchorage to a 

 variety of parasites and messmates ; but, fortunately, few or it 

 may be none of the strictly human parasites require to pass 

 through these intermediate bearers. Distoma crassum is possibly 

 an exception. Save the cuttle-fishes, not many evertebrated 

 animals are infested by sexually-mature worms. One of the 

 most notable exceptions is that of a nematoid infesting bees. 

 This worm was known to John Hunter, who spoke of it as 

 " the animal that breeds in the humble bee." In the year 

 1836, M. Leon Dufour first applied the term Sph&rularia to 

 this remarkable worm, which he discovered in the abdominal 

 cavities of two species of bee (Bombus terrestris and B. hor- 

 torum). The worm was subsequently found by Von Siebold in 



