670 THE POPULAR SCIENCE MONTHLY. 



siderably above the sea. If this be true, not only is the proposed 

 inland sea an impossibility, but we must also i-elegate to the domain 

 of fable the accounts of the great lake of Tritonis, or assign it to 

 another locality. 







ANIMAL PAKASITES AND MESSMATES. 



THE fight for a foothold in the animal world brings the combatants 

 into many strange relations, few of which are more curious and 

 interesting than those existing between the creatures popularly known 

 as parasites and the animals which furnish them support. In these 

 relations all grades of pauperism and criminality are represented. 

 There is the miserable wretch that lives entirely at the expense of 

 others, finding it easier to die than to help himself; the poor weak- 

 ling, willing enough to do what he can, but sure to starve to death 

 if left wholly unassisted ; the petty thief that sneaks into his neigh- 

 bor's premises and steals a portion of his store ; and the audacious 

 robber that boldly appropriates another's substance, and not unfre- 

 quently adds murder to his list of crimes. In his entertaining and 

 instructive work on "Animal Parasites and Messmates," ' from which 

 this article and its illustrations are mainly taken. Van Beneden makes 

 these different degrees of dependence the basis of a rough but con- 

 venient classification, by which he separates, what Iiave hitherto been 

 known as parasites, into three groups, named respectively messmates, 

 Tnutualists, and parasites. 



The messmate is one that takes his place at his neighbor's table 

 to partake with him of the product of the day's toil. He does not 

 live directly at tlie expense of his host, but, abiding with him, obtains 

 thereby better opportunities for securing a supply of food. This mode 

 of getting a living is very common, and a curious thing about it is 

 that animals comparatively high in the scale of organization do not 

 scruple to quarter themselves upon others of much inferior giade. The 

 fish known to naturalists as fireasfer lives in this relation. He takes 

 up his lodgings in the digestive tube of a holothurian, and, regardless 

 of the rules of hospitality, appropriates a portion of all the food that 

 enters. He thus manages to get himself served by another better 

 provided than he is with the means of fishing. Dr. Greef found at 

 Madeira a holothurian over a foot long, in which one of these fishes 

 was enjoying a peaceful and vigorous existence. Other fishes besides 

 the fireasfer have been found in similar quarters ; indeed, the situation 

 appears a very favorable one for this mode of life, since not only 

 fishes but crustaceans here take up their abode, sometimes in con- 

 siderable numbers. Prof. Semper has seen holothuriae in the Philip- 



' No. XIX. " International Scientific Series," New York, D. Appleton & Co., 18Y6. 



