ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 51 



power of stopping the development of these organs, the Termites are 

 able to hasten their maturation. 



Poison - apparatus of Mosquito.* — Prof. G. Macloskie gives an 

 account of the poison-apparatus of the Mosquito. There are two sets of 

 glands, one on each side in the antero-inferior region of the prothorax ; 

 each consists of three glands, two of which are of the usual aspect of 

 salivary glands, and resemble in structure, though they are not propor- 

 tionately as long as the single salivary glands of the house-fly. The 

 third or central gland of each set is evenly granular and stains more 

 deeply than the others ; it is this which, no doubt, has the function of 

 secreting the poison. Each gland is traversed throughout by a fine 

 ductule, and the three unite at the base to form a common duct, which 

 is one of the branches of the veneno-salivary duct. The secretion of 

 the lateral glands dilutes the poison. The single main duct passes to 

 the reservoir at the base of the hypopharynx. The pressure on the sur- 

 rounding parts is sufficient, when the mosquito inserts its piercing 

 apparatus, to propel the poison through the tubular axis of the hypo- 

 pharynx into the wound. The distal orifice of the hypopharynx is sub- 

 apical and not exactly terminal ; the tip is flattened and sharp so as to 

 enter easily and enlarge the wound made by the adjoining organs. 



S, Arachnlda. 



Anatomy of Hydrodroma.t— Dr. E. v. Schaub gives a detailed 

 account of the anatomy of this Hydrachnid, one of the characters of 

 which is the possession of a small highly chitinized dorsal shield under 

 the skin between the eyes. 



The matrix of the chitin of the integument is a thin layer of homo- 

 geneous tissue, which is broken by irregular lacunae; this matrix is 

 also the seat of the pigment which is collected at nodal points, and 

 contains distinct nuclei. The dorsal shield not only serves as the point 

 of origin for a number of muscles, and especially those of the oral cone, 

 but also as a protection for the subjacent sensory organs. The dermal 

 glands, peculiar to the Hydrachnida, are, in Hydrodroma dispar, arranged 

 in four longitudinal rows over the back ; their tunica propria is extremely 

 thin, and is supported by a network of thin chitinized ridges ; the secre- 

 tory cells are divided into two hemispherical groups ; they open by a 

 cleft, which is surrounded by a strong chitinous wall. On the legs 

 there are a number of very variously formed chitinous set^e, all of which 

 have an internal canalicular cavity, which, with the exception of the 

 swimming hairs, is indicated by a thin layer of red pigment. The 

 author does not agree with Haller in his division of the hairs into 

 tactile and olfactory organs, though he has no doubt of their general 

 tactile sensibility. 



Like all other Hydrachnids, Hydrodroma has the basal joints of the 

 pedipalpi fused to form a suctorial proboscis, which corresponds to the 

 maxillae, and incloses the mandibles ; this apparatus is briefly described. 

 Above it are a pair of oval orifices, which were first recognized by 

 Kramer as the stigmata of the tracheal system ; they lead directly into 

 a tube which is • 008 mm. thick, formed of colourless and homogeneous, 

 but hard, chitin. The two tubes pass into air-reservoirs formed by tho 



* Amer. Natural., xxii. (1888) pp. 884-8. 



t SB. K. Akad. Wiss. Wien, xcvii. (1888) pp. 98-154 (6 pis.). 



E 2 



