962 



SCIENCE. 



[N. S. Vol. XII. No. 313. 



move, molt and pass their excretions, have 

 been mooted points. Cuvier thought that these 

 larvsB breathed by placing their spiracles in rela- 

 tion with those of the host insect. Gerstaecker, 

 in 1863, came to the same conclusion. Ratze- 

 burg attributed a respiratory function to the anal 

 vesicle in certain Braconids and to the caudal 

 appendage in the Ichneumonids. Boisduval 

 concluded that they do not take nourishment 

 through the mouth, that they do not breathe 

 and that they void no excrement, the larva 

 being analogous to the foetus in mammalia, 

 which lives the life of the mother. Newport 

 described the larvfe of certain Ichneumonids as 

 having no anus, the rectum and its orifice being 

 rapidly developed at the final larval change. 

 The older authors thought that these larvae at- 

 tack only the fatty tissues of the host. Bugnion 

 states that Encyrtus nourishes itself exclusively 

 on the lymph. Ganin has observed a curious 

 hyper-metamorphosis in certain egg parasites 

 of the family Proctotrypidse. Marchal has 

 made some extraordinary observations upon 

 other Proctotrypids, showing that one form 

 (Trichacis) develops in the nervous system of 

 Cecidomyia, while Polygnotus develops in the 

 digestive tract of the same host. 



Seurat, in the paper under consideration, re- 

 ports the results of investigations which he has 

 conducted upon members of three families of 

 parasitic Hymenoptera. He has studied the 

 Braconids, Apanteles glomeratus in the common 

 European cabbage worm, Aphidiua faharum in 

 the common Aphis rumicis and Doryctes gallicus, 

 an external feeder on a wood-boring larva. 

 The Ichneumonids studied are two internal 

 feeders, Mesochorus vittaior and Hemiteles ful- 

 vipes, and one external feeder, Xylonomus prse- 

 catorius. Among the Chalcidids he has studied 

 Diplolepis microgastri, an internal-feeding hyper- 

 parasite in Microgasterid cocoons, and an ex- 

 ternal feeder, Torymus propinquus, which lives 

 in Cecidomyiid galls, feeding externally on the 

 Cecidomyiid larvse. The work has been done 

 with the greatest care and the conclusions at 

 which he arrives are of authoritative value. 

 They are summarized as follows : 



(a) Manner in which larvet nourish themselves. — 

 The external and internal larvse are formed 

 with very sharp mandibles. The internal forms 



use them in order to pierce the tissue of the 

 host ; the external ones to pierce the skin of the 

 host, making a delicate orifice which permits 

 them to suck up the tissues. The digestive 

 tube is always remarkable by the presence of 

 the very voluminous stomach closed behind (this 

 proves to be the rule in the young larvse of 

 Hymenoptera) and which serves as a sort of 

 storehouse for food which is digested later. A 

 small quantity of food digested at once suffices 

 for the immediate wants of the larva. The 

 voiding of the excrement only takes place in 

 the interior of the cocoon, the stomach not 

 opening until that time. The stomach of the 

 larva contracts and dilates very rapidly, these 

 movements probably favoring the ingestion of 

 food. The materials which the parasite borrows 

 from its host are varied. In certain cases 

 {Apanteles glomeratus) the fat, the blood and the 

 lymph only disappear. In the majority of cases 

 the parasitic larva devours everything except 

 the skin and trachese. The parasite respects 

 the viscera up to the last limit and only sacri- 

 fices them at the end. He has seen in certain 

 cases the larva devour several host insects. 



(6) Respiration. — The problem of the mode of 

 respiration is a puzzling one with internal feed- 

 ing larvae. External larvse are provided with 

 spiracles permitting the entrance of air. The 

 respiration of the young internal larvse not yet 

 provided with trachese filled with air is eflected 

 by osmosis through the skin by the whole sur- 

 face of the body. The larvae furnished with an 

 anal vesicle or caudal respiratory appendage 

 breathe with the skin of these organs as well as 

 with the whole surface of the body. These ap- 

 pendages are lacking, however, in certain cases, 

 as in the Aphidiinae, the Chalcididae, etc. The 

 trachea? are not slow in appearing elsewhere. 

 The tracheal system is complicated in accord- 

 ance with the needs of the larva. It is entirely 

 closed and the entrance of the air is made 

 through the skin and the very fine membrane 

 of the ultimate tracheal branches. The entire 

 surface of the skin is carpeted with an ex- 

 tremely rich net-work of fine tracheae which 

 facilitate the accomplishment of this function. 

 The hypothesis of the osmosis of air from the 

 liquid tissues of the host through the body wall 

 of the parasite and the cover of the tracheae is 



