ZOOLOfiY AND BOTANY, MICROSCOPY, ETC. 379 



stig-mata, the small simple eyes of the female, the absence of a circulatoiy 

 system, the presence and " transmission " of symbiotic micro-organisms, 

 the occurrence of parthenogenesis, and the scarcity of males in many 

 species. 



Parasite of White Rust Coccid.* — A. Berlese and G. Paoli describe 

 a minute end(jphagous Chalcidid from Madeira, Prosjmltella loiinshuryi 

 sp. n., wliich promises to be an effective parasite of the Coccid Clirysom- 

 plialus dktyosperml, which does serious damage (as hianca-rossa) to 

 orange-trees. The antagonist attacks not only the adults Init the 

 nymphs, and large numbers were found parasitized. 



Rectal Grills of Larval Dragonflies.t— R. J. Tillyard has studied 

 the respiration of the larvae of Anisopterid dragonfiies, which is dis- 

 charged by means of a secondarily closed tracheal system, though the 

 spiracles of the thorax, at any rate, can, under certain circumstances, 

 be made to function as orifices of inspiration if the larva leaves the 

 water„ In the Zygoptera there are caudal gills, in the Anisoptera rectal 

 gills. In the Simplex system of rectal gills the rectal wall is thrown 

 into six main longitudinal folds supported by cross folds ; in the Duplex 

 systena the main folds are functionless or suppressed, and the cross 

 folds become separate gills in six double rows. The gills are further 

 classified, but whatever their type they are delicate eversions of the 

 rectal wn^li into the rectal cavity. 



Each gill includes eight elements : the cuticle, the epithelial 

 syncytium, the pigment, the basal pad, the hypobranchial tissue, the 

 blood plasma in the narrow blood spaces, the capillaries, and the larger 

 trachea and efferents. These are discussed in turn. The pigment, the 

 basal pad, the hypobranchial tissue, and the blood plasma are accessory 

 to the essential process of respiration, and the larger tracheae function 

 only as receivers of oxygen from the capillaries. The essential problem 

 is how the cuticle, the epithelial syncytium, and the tracheal capillaries 

 combine to extract oxygen from the water in the rectal cavity. 



According to one theory the gas simply diffuses through the delicate 

 wall of the gill, as is suggested by the thinness and deHcacy of the 

 cuticle, the alteration of the undifferentiated rectal epithelium into a 

 thin syncytium, the extreme fineness of the tracheal capillaries, and the 

 complete absence of the spiral thread, the fact that the capillaries are 

 embedded in the syncytium close to the surface, and that they all form 

 complete loops, there being no circulation of gas in a definite direction, 

 but simply a passage of gas from all points inwards towards the efferent 

 trachere. The diffusion theory of Lowne and Ris is supported by the 

 author's observations. 



Tillyard considers (1) the method of filling the tracheae with gas 

 in the newly-hatched larvse (the filling coming not from the rectum 

 but from in front) which precedes the beginning of rectal respiration ; 

 (2) the process of diffusion during larval life; (3) the passage of 

 oxygen along the tracheal tube ; (4) the elimination of nitrogen ; and 



* Eedia, xi. (1916) pp. 305-7 (2 ligs.). 



t Proc. Linnean Soc, New South Wales, xl. (1915) pp. 422-37 (1 pi.). 



2 D 2 



