BIOLOGY OF LIMNEEIUM VALIDUM. 89 



well developed in all three larval stages in the case of Limneriutn^ 

 we hesitate to apply it in entirety to this species. We do not believe, 

 however, that the larvaj of Limnenum while small actively attack 

 and devour any of the solid tissues of the host including the fat- 

 bodies, but rather institute pathological changes whereby these tis- 

 sues become available for food. The first tissues to be broken down 

 are the fat-bodias, whereas the vital organs, including the digestive 

 tube, resist dissolution until the last. The very apparent, earl}^ dis- 

 appearance of the fat-body in parasitized caterpillars probably ac- 

 counts for the old theory that the parasite consumes it directly. The 

 parasite certainly does consume the fat-body, but only after it has 

 been broken down. We have often noticed this condition of the fat- 

 body in apparently healthy caterpillars that harbored the early stage 

 of almost any hymenopterous jDarasite. In such cases the fat-bodies 

 were broken down more or less completely into their component 

 parts, and the blood of the host was filled Avith the perfectly globular 

 fat cells of varying sizes, and sometimes of a truly enormous size for 

 individual cells. These small, solid particles, we believe, are as 

 readily eaten by the larva; of Limnerhnn., at least, as the fluid medium 

 in which they float about within the body of the host. The mouth- 

 parts in the first and second stages of Limnerlum are admirably 

 adapted for this purpose, being in fact a sucking apparatus, with 

 strong, pointed mandibles, so placed as to aid in swallowing small, 

 solid particles. In the third stage the mouthparts are still essen- 

 tially sucking, but as the mouth opening is surrounded by chitinized, 

 supporting or possibly rasping ridges, there is some ground for be- 

 lieving that even solid tissues may now be taken in, even before they 

 have been wholly disintegrated. When the parasite reaches this 

 stage, the host has become somewhat weakened, its fat-body having 

 been almost entirely, and its body fluids greatly, depleted. Unlike 

 the condition produced by some larva^ of tachinids at this stage in 

 their development, the remaining tissues never dissolve into a putrid 

 or semiputrid mass, but at all events remain clear and wholesome. 

 To just what extent the tissues are broken down before being con- 

 sumed has not been definitely determined, but we believe usually to 

 a semiliquid condition in the case of Limneiiiim,. A caterpillar for- 

 saken by a larva of the Limnenum was closely examined, and a 

 small amount of tissue was found at the posterior end of its body. 

 This tissue was probably the remains of the muscles of that region, 

 and appeared to be of a mucilaginous consistency. 



RESPIRATION OF THE LARVA IN THE THIRD STAGE. 



The shortening of the tail appendage in the second stage and its 

 entire disappearance in the third stage must necessitate a gradual 

 change in the respiratory habit of the larva, if, indeed, the tail is a 



