48 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and after 45 minutes' exposure in carbonic oxide. Prussic acid vapours 

 and nitrous acid fumes killed quickly, though the Colorado beetle 

 resisted the attacks of the former more stubbornly than any other 

 insect. Dense chlorine was also very fatal, but the beetles lived in 

 an atmosphere overj)oweringly odorous of it for an hour, and partially 

 recovered on their release. In nitrous oxide the beetles lived 2 hours 

 only, while the young of the common grasshopper {Caloptenus femur- 

 ruhrum) were confined 2 hours, and were but little affected ; Noctua 

 died in 1^ hour. In illuminating gas the beetles were instantly 

 prostrated, but after an hour's immersion some recovered ; croton bugs 

 (Ectobia germanica) recovered after h an hour, the young grasshoppers 

 after an hour, and flies after 5 minutes. 



Mouth-organs of Sucking Insects.* — Basing his remarks on the 

 Aphidce and Hemiptera, and especially on the Diptera, Dr. K. Kraepelin, 

 in a preliminary account of his investigations, finds these three groups 

 distinguished by characteristic arrangements of their sucking-tube. 

 In Bomhiis the tube is composed of the labial palps and the maxillae, 

 which are connected with them by strips of substance ; near their 

 lower margin the paraglossfe intervene between the palps and the 

 maxillae. The half-canal formed by the upward curve of the margins 

 of the labium gradually disappears towards the posterior part of 

 the latter, and allows liquid which has passed down it to escape 

 between the labium and maxillee into the mouth, at the point of origin 

 of the paraglossae. Besides the tactile hairs certain peculiar clavate 

 pale hairs are placed on the apex of the labium, which appear from 

 observations to be analogous to the olfactory hairs of the inner pair 

 of antennae of Crustacea, and as they cany a minute opening at 

 their ends, must be considered as either gustatory or olfactory 

 organs. 



Like that of butterflies, the sucking-tube of the Hemiptera is made 

 up exclusively of the two maxillae, which unite in such a way as to 

 form a double cylinder, the upper division of which carries the food, 

 the lower the salivary secretion. The mandibles lie by the side of 

 the maxillae, and can move about on the tube. The end of the labium 

 is provided with terminal nervous organs. In the proboscis of the 

 Diptera the sucking-tube is formed mainly by the labrum, which con- 

 sists of a demi-canal, closed below partly by the mandibles which are 

 connected with it by a groove-and-ridge joint and partly by the hypo- 

 pharynx, which runs below the mandibles, carrying the salivary canal ; 

 on each side below the hypopharynx lie the masillte. 



Dealing with the mouth of Biptera at greater length, Kraepelin 

 dissents from Dimmock's and Meinert's view, that the labrum is here 

 made up of the labrum proper and the epiiDharynx ; the paired organs 

 described by Meinert in Hippohosca, &c., as an independently formed 

 epipharynx, are here regarded as enormous developments of the cheeks. 

 The muscles of the proboscis in Musca consist of — (1) Retractor of 

 the fulcrum, and thus of the whole proboscis. (2 and 3) Extensor and 

 flexor of the labium. (4 and 5) Elevator and depressor of the 



* Zool. Anzeig., v. (1882) pp. 574-8. 



