THE CHALCIDOID GENUS PERILAMPUS. 55 



Perilampus versus Dibrachys. 



Another exceedingly curious complication was observed in the 

 winter of 190S-9 in an instance where a cocoon of Limnerium validum 

 had been attacked by Perilampus and later by Dibrachys houcheanus 

 Ratzeburg. The larvae of the latter parasite fed externally and gre- 

 gariously, and hibernated without transforming to pupse. So soon 

 as its original host was destroyed, the Perilampus planidium, not to 

 be outwitted, calmly proceeded to take up a position internally in 

 one of the Dihracliys larvae. The particular larva bearing this plani- 

 dium was killed and preserved, but in another instance a very small 

 Perilampus adult issued from a puparium of Varichseta from which a 

 number of Dihracliys adults had emerged some time before, and there 

 is no doubt that it completed its transformations as a parasite on this 

 host. With the exception of Melittohia, which from its very small 

 size would likely prove unsuitable as an ultimate host, there is no 

 known hymenopterous hyperparasite likely to attack the puparia 

 of Variclis&ta or the cocoons of Limnerium, which might not serve as 

 well as Dihracliys as a host for Perilampus. The planidium is admi- 

 rably fitted to triumph over adversity, and shows the part of wisdom 

 in not causing the death of its host until it is ready to complete its 

 transformations. If, for example, it had the habit of killing its host 

 in the fall, and of hibernating as a full-fed larva, after the manner of 

 Dibrachys, the latter might easily turn the tables and emerge victo- 

 rious from the conflict. 



PEHILAMPUS, "SPECIES A." 



(Figs. 30, 31.) 



In the course of the investigations upon the genus Perilampus, two 

 kinds of planidia have been found parasitic upon Limnerium validum, 

 which, wdiile belonging to the same general type, are quite different 

 in structural detail and apparently represent different species. One 

 of these, the commoner one, is Perilampus hyalinus, which has been 

 treated rather fully in the preceding pages. The other species we 

 have never succeeded in rearing through to the adult, so are unable to 

 give it a specific name at this time. In length it is rather shorter 

 than hyalinus, measuring on the average about 0.24 mm., but is 

 comparatively greater in diameter through the anterior segments. 

 The color is usually somewhat darker than that of hyalinus. In P. 

 hyalinus the head of the planidium is notched or emarginated and 

 elevated posteriorly, but in this species the posterior margin is con- 

 tinuous. The mandibles are heavier and considerably less curved, 

 and the recurved hooks on the top of the head are also considerably 

 larger. The ambulatorial spines are very much less developed than 



