TRUE GUESTS, ECTO- AND ENTO PARASITES. 



411 



progenitive instincts, a modification which during the course of phy- 

 logeny has become differentiated from the more general instincts of 

 this type." He believes that we are justified, therefore, in speaking of 

 " special symphilic instincts," which, from the nature of the definition, 

 would be hereditary. It will be noticed that Wasmann fails to distin- 

 guish between the "instinct stimulus," the "instinct action" or objec- 

 tive aspect of instinct and its subjective aspect, the " instinct disposi- 

 tion." Escherich (1898^ et al.) has repeatedly attacked Wasmann's 

 amical selection hypothesis, on the ground that there is nothing to show 

 that the ants exercise any selective 

 choice among their guests or that there 

 is anything corresponding to " special 

 symphilic instincts." The philoprogeni- 

 tive instincts are quite sufficient to ac- 

 count for the phenomenon, which is 

 merely a parasitic disease, or instinct 

 aberration, comparable to the rearing of 

 the young cuckoo by its foster parents, 

 or the rearing of puppies by cats, of 

 kittens by hens, etc. In these cases we 

 do not postulate a special hereditary in- 

 stinct modification, but a simulation of 

 the normal stimulus by an abnormal ob- 

 ject. The instinct action is normal, but 

 adapts itself to the changed conditions 

 and there is nothing to indicate that the 

 instinct disposition has undergone any 

 phylogenetic change. Wasmann's con- 

 tention is disproved, as Escherich has 

 pointed out, by the way in which the ants 

 unearth the Lomechusa pupse. 



In his attempt to substitute amical for natural selection Wasmann 

 also overlooks the fact that ants live in opulence, to use Janet's expres- 

 sion, compared with solitary animals, and are therefore able to support 

 a host of parasites on what may be called their large margin of vitality, 

 without serious danger to the existence of the species. In fact, there 

 is no essential difference between the behavior of F. sanguined towards 

 Lomechusa and that of other hosts towards their respective parasites 

 of no matter how extreme a type, for all organisms nourish with their 

 juices the parasites that manage to implant themselves in their tissue?, 

 just as the ants feed the Lomechusa with regurgitated food. Was- 

 mann's objection would apply not only to all parasites but to all precla- 



FIG. 247. Parasitic mites of 

 Lasius tui.rtiis. (Janet.) A. 

 Uropoda ovalis fixed in its nor- 

 mal position by an adhesive 

 uropod to the extensor surface 

 of the middle femora of the 

 Lasius worker : B, Urodiscella 

 philoctena in its normal posi- 

 tion, attached by one of its fore- 

 legs to the pectinated spur of 

 the fore tibia of the Lasius 

 worker. 



