140 PARASITES OF GTPSY AND BROWN-TAIL MOTHS. 



many caterpillars upon which the eggs had actually hatched, but 

 from which no parasites were reared. 



That this explanation may serve in part to elucidate the mystery 

 is also true, but still later observations have shown conclusively 

 that the parasite larvas may gain entrance into their host and yet 

 fail to mature. Two explanations have grown where one was deemed 

 sufficient, as the result of certain technical studies winch have been 

 made at the laboratory during the past year. Mr. P. H. Timberlake 

 and, later, Mr. W. R. Thompson have thoroughly demonstrated the 

 fact that a parasite larva gaining lodgment in an unsuitable host 

 may die, and its body may be in great part absorbed through action 

 of the phagocytes without causing the host obvious inconvenience. 

 This very likely takes place with Tachina mella in its relations with 

 the gipsy moth and is probably a better explanation of its failure to 

 become an effective parasite than any other which has yet been put 

 forward. 



Mr. Thompson also discovered another most remarkable and 

 peculiar phenomenon in connection with parasitism hy those tachi- 

 nids the larvae of which inhabit integumental funnels similar in 

 character to those formed by Tachina. These funnels appear to be 

 formed as a direct result of the tendency of the skin to grow over 

 and heal the wound caused by the entrance of the tachinid maggot 

 into the body of the host. This wound is kept open by the larva 

 itself, and as a result the growing integument takes the form of an 

 inverted funnel, more or less completely surrounding the parasitic 

 maggot, winch continues to breathe through the minute orifice in its 

 apex. When the caterpillar molts the old skin is usually torn away 

 from around this opening, leaving the maggot in situ and unaffected, 

 but occasionally its attachment to the funnel may remain so strong 

 as to result disastrously for the maggot, and the whole funnel, maggot 

 included, may be withdrawn. Thus, not merely the eggs may be 

 molted off, but the internal feeding maggots which have hatched 

 from the eggs may be molted out and perish. 



ACH^ETONEURA FRENCHII WlLL. 



A very few specimens of this species have been reared from time 

 to time in the course of the work at the laboratory. It is probable 

 that the species is synonymous with that mentioned by Forbush 

 and Fernald under the name of Achdetoneura ferrwildi. 



EXORISTA .BLANDA O. S. 



Occasionally reared as a parasite of the gipsy moth. 



