ACANTHOCEPHALA. 789 



Aitliougli the development of the EchinorJujncJiiis of the hog 

 has never been fully traced, there can be little doubt that its 

 mode of development is precisely similar to that known to occur 

 in otlier members of the genus. Dr. Guido Wagener has fur- 

 nished us with some admirable illustrations of tlie eggs and 

 embryos of various species (Sieb. and Koll., Zeitsch. vol. ix.), but 

 it remained for Leuckart to explain that these creatures during 

 growth exhibit the characteristic phenomena of alternate genera- 

 tion {Gott. Nachrichten, 1862). His experimental investigations 

 were chiefly made with E. proteus and E. fiUcollis. Professor 

 Leuckart caused some fresh water crustaceans (Gavwiari) to 

 swallow the eggs of these small thorn-headed worms, and he had 

 the satisfaction of observing that in a few days the embryos 

 quitted their egg-shells and passed into the bodies of the unsus- 

 pecting intermediary bearers. After a series of further changes 

 (which Leuckart regarded as comparable to those of a true 

 alternate generation, and not simply metamorphotic), the young 

 parasites rapidly increase in size ; the original skin of the 

 embryo being cast off " as soon as the ecliinorhynchus occupies 

 the whole interior of the embryo." The young parasites acquire 

 sexual organs whilst still lodged within the intermediary bearers, 

 so that, within about a week after they are transferred to the 

 intestinal canal of their proper and ultimate piscine host, their 

 development into the adult state is completed. What ordinarily 

 takes place in the case of these echinorhynchi of the fish must 

 more or less appertain to the echinorhynchi of the hog. Swine, 

 as we all know, are not very particular as to what they eat or 

 drink, consequently they have abundant opportunities of swal- 

 lowing insects, gammari, entomostracous crustaceans, or other 

 minute creatures which are destined to harbour the larvte of 

 acanthocephalous parasites. 



According to Schneider the eggs of the Ecliinorliynclius gigas 

 are discharged in the faeces of the pig, which harbours the 

 sexually mature adult. The eggs are devoured by maggots, 

 and, reaching the stomach, are hatched. The embryos, which 

 are provided with spines, bore their way into the body cavity of 

 the maggot where they develop a young Echinorhynchus in their 

 interior. The maggots are in turn devoured by the pig, in 

 which the Echinorhynchus again reaches sexual maturity and 

 produces ova. 



