ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 569 



Dermal Sensory Organ of Insects.* — Dr. 0. vom Eath has publislied 

 in extenso an account of his observations on the dermal sensory organs of 

 Insects, the preliminary notice of which we have already reported,! ^s 

 to the physiology of these organs little is definitely known, and as the 

 structure of the various organs is essentially the same, nothing can be 

 concluded therefrom. The most important position is that of the 

 antennae ; here we find sensory hairs, cones, and membranous canals. 

 With most authors. Dr. vom Eath thinks that the olfactory sense is 

 located in the sensory cones, and perhaps also in the membranous 

 canals, and that the hairs have a tactile function. The function of the 

 canals appears to be one which is well developed in a few Insects only, 

 as they are only occasionally present ; where they are found they are 

 present in large numbers ; it is not likely that they are of an auditory 

 nature, and it is more probable that they serve for the perception of 

 definite odours, or fulfil an unknown function. 



It is only in rare cases that it can be definitely asserted that there is 

 an orifice at the anterior end of the cones, and this point seems therefore 

 to be of little physiological significance. The chitin at the anterior end 

 of the cone is in any case thin and pale, and is probably affected by 

 chemical and physical influences ; treatment with dilute potash easily 

 dissolves the chitinous membrane, when the cone is laid open. Where 

 the cones stand in chitinous pits and do not reach the surface we cannot 

 suppose that there is any tactile function, but rather an olfactory. If 

 this be so, and if there are different kinds of cones, we may suppose that 

 these have somewhat different functions. It is possible that some serve 

 for the perception of the feeble odours of distant objects, and others for 

 those that are nearer. 



On the palpi cones and hairs are alone found ; Ley dig was certainly 

 justifi.ed in declaring that their anatomical structure shows that the 

 palpi have the same or similar functions to the antennee. Dr. vom Eath 

 believes that the cones are olfactory organs, and probably perceive not- 

 distant odours. The cones on the maxilla, labium, epipharynx, and 

 hypopharynx seem to be gustatory organs. 



Sub-aquatic Respiration.^ — Herr E. Schmid has studied minutely, 

 in Donacia crassijjes, the mode of breathing to which Siebold called 

 attention as common among the larv® and pupse of beetles, i. e. extract- 

 ing air from the air-passages of submerged water-plants. 



Pupa-cases, found by him attached to the roots of the water-lily, 

 were observed to be filled with air. A hole in the side of the case 

 next the root corresponded exactly to a deep canal passing through many 

 of the air-passages of the root. This canal had evidently been bored 

 by the insect, and the consequent pressure had caused the air to pass into 

 the cocoon. The larvae have two main tracheal trunks opening into two 

 sickle-shaped chitinous appendages on the abdomen. These appendages 

 are used, apparently, for boring into a plant so as to allow air from its 

 air-passages to pass into the tracheae of the insect. When the insect 

 escapes from the cocoon it is borne to the surface by the air surrounding 

 it and imprisoned in the hairs on its ventral surface. 



The same mode of breathing may be observed in the genus Haemonia. 



* Zeitschr. f. Wiss. ZooL, xlvi. (1888) pp. 413-54 (2 pis.). 

 t See this Journel, ante, p. 210. 



X Entom. Zeitschr., xxxi. (1887) pp. 325-34. Cf. Naturforscher, xxi. (1S88) 

 p. 193. 



