274 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ter-crab. The commensals of the first series carry with them 

 the marks of their servitude ; those of the second have no 

 feature by which they can be specially recognized. The se- 

 ries of uniformly fixed commensals he calls oikosites, and di- 

 vides them into perpetual, temporary, and while young. The 

 free commensals he calls ccenosites, whether inhabiting the 

 digestive canal, the mantle, or the outside. The true para- 

 sites, or those that feed upon their hosts, are also divisible 

 into free and attached, the former being classified by Van 

 Beneden into those that are free during their whole lives, as 

 leeches, fleas, etc., and those that are free for part of their 

 lives only. These may confine themselves to one host, 

 whether while young, as the ichneumons, or when adult, as 

 the lerneans ; and they may have several hosts while young, 

 as the distomas and cestoid worms. To this general group 

 the name of phagosites has been applied, and they are really 

 the guests of the hotel, which profit only by the table of the 

 host, while the others have at the same time both food and 

 lodgment. 



These latter are divided into three essential classes, those 

 (xenosites) that travel about and arrive at their destination, 

 like pilgrims, with a definite object before them, being para- 

 sites in transit. They are also agamous, and are lodged in 

 the close cavities like the brain, the muscles, or the serous 

 membrane. They do not grow after they are introduced, 

 but assume the character of a cyst, waiting in a lethargic 

 state the day of their awakening in the stomach of a new 

 host. These generally, .when liberated by the digestion of 

 the external covering in the stomach of another animal, as- 

 sume some other transformation. 



The next division of these internal parasites is that called 

 the nolosites, embracing such as, having arrived at their des- 

 tination, can give themselves up to the business of reproduc- 

 tion, taking the attributes of sex in the most appropriate 

 organs at the end of their journey. The third, or the piano- 

 sites, are those that have gone astray, and can never arrive 

 at the end of their journey. These never quit their retreat, 

 especially such of the agamous worms as are confined to the 

 voracious fish, like the sharks, etc., which have scarcely a 

 chance of passing with their host into the stomach of the 

 animals for which they were destined. Mem. Acad, de Bel- 

 gique, XXXVIII., 1871. 



