WANDERINGS OF ECHINORHYNCHUS AND ITCH-MITES. 139 



It is self-evident that the consequences of such boring out of or 

 into the body-cavity must be much more deep-seated and dangerous 

 than those which result from the mere wandering of an embryo. The 

 size and very appreciable movements of the parasite usually produce 

 in man a very intense peritonitis, which has a specially rapid and 

 fatal course in those cases in which other foreign substances have 

 passed through the walls of the intestine along with the worms. 



Thread-worms, however, are not the only intestinal worms which 

 are capable of such migrations. These are even more frequently 

 undertaken by the Acanthocephali, which, with their powerful hooks 

 studding the sides of a retractile proboscis, are specially adapted for 

 such work. Even the Echinorhynchus gigas of the pig, although 

 several millimetres in diameter, can by means of its boring ap- 

 paratus perforate the walls of the intestine. We know also of similar 

 wanderings, even among the tape-worms not only in the case of Tcenia 

 solium, but also of other species not provided with hooks. Thus Tcenia 

 plicata not unfrequently passes from the alimentary tract of the hare 

 or rabbit to the body-cavity, without, however, exciting the usual 

 serious symptoms, since these hosts are but slightly liable to peri- 

 tonitis. Goze found in one case 1 " a small aperture closed by thick- 

 ened margins, by which the worms had made their exit, and which 

 could only be observed internally on the villous surface." He further 

 cites the case of a diver infested with Ligula, some of which had 

 penetrated the intestinal walls. 2 In its larval state the Ligula, as 

 is well known, inhabits the body-cavity of white-fish, especially of the 

 bream, and towards the end of August it often breaks through the 

 body -wall "ventrally, laterally, or dorsally, or even sometimes 

 on the head or near the tail. The point where the perforation has 

 taken place is somewhat swollen, the skin becomes thin, and the 

 blood-covered wound which is left is longitudinal, like that of an 

 artery." 3 Steenstrup observed a similar phenomenon in the Schisto- 

 cephalus of the stickleback, but in this case the injury generally 

 proved fatal.* 



In contrast to these only occasional wanderers, there are also 

 adult parasites which are continually moving. Chief among these is 

 the itch-mite (Sarcoptes scabiei), which burrows in all directions ill 

 the epidermis (Figs. 86 and 87), and by the perforation of the papillae 

 of the cutis causes the painful eruptions which were for many 

 centuries considered as a special disease the itch. 



1 " Versuch einer Naturgesch., u.s.w.," p. 367. 



2 Ibid., p. 25 and p. 185. 



3 Bloch, " Abhandl. u. s. w.," p. 2. 



* See the observations cited on page 25, and also v. Baer, " Ueber Linnes im 

 WasRer gefundene Bandwttrmer," Verhandl. naturf. Freunde Berlin, Bd. i., p. 388, 1829. 



