ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 347 



dorsally, and in part laterally. The kidney as a whole lies in the 

 median dorsal part of the mussel wedged in between the insertion of the 

 foot and gills and the floor of the pericardium in the form of a club, 

 which widens and thickens from its oral tips towards the anus ; and, in 

 the space between the pericardium and the posterior adductor, stretches, 

 as the nephridial coil, from one half of the mantle to the other. The 

 two nephridial loops are separated by the sinus venosus and the re- 

 tractor pedis. The length of the whole organ is about a third of the 

 length of the animal. Its perfectly straight longitudinal axis lies 

 obliquely to the longitudinal axis of the mussel. 



The various parts of the organ are described in detail. The author 

 considers that the smooth communicating duct enclosed by the elastic 

 renopericardial wall, forms, in constrast to the much folded coils and 

 sacs, a morphological unit which may be distinguished as the " excretory 

 bladder." 



Arthropoda. 

 «• Insecta. 



Respiratory System in Water-beetles.* — Frank Brocher describes 

 two types of tracheae in adult water-beetles. Besides the ordinary 

 tubular forms there are others with a slightly developed spiral thread. 

 They are not to be confused with vesicular tracheae which have no 

 chitinous thread. In Dytiscus and Hydrophilus the lumen of the large 

 longitudinal tracheae is not continuous. There is a large air-chamber 

 on each side of the body between the mesothorax and the metathorax, 

 which is in close association with the yellowish muscles of flight. In 

 the tetanic vibratory contraction of these muscles, the tracheae among 

 the fibrils are subject to continuous compression and relaxation, and 

 the reservoir may have to do with the regulation of the pressure. 



Brocher confirms Camerano's statement that there are respiratory 

 movements in the metathorax, and gives full details proving this. In 

 Hydrophilus and Dytiscus the main respiratory movements are localized 

 in the metathorax. In Hydrophilus inspiration appears to be as active 

 as expiration, and the inspiratory muscles are stronger than those con- 

 cerned in expiration. 



Tracheo-parenchymatous Organ of Aquatic Hemiptera.| — Ch. 

 Ferriere has studied this peculiar whitish organ which occurs in the 

 thorax of some aquatic Hemiptera, such as Xepa, Ranatra, and Naucoris. 

 It is a paired structure, disposed on each side of the dorsal vessel ; it is 

 formed of a peculiar fibrous tissue, and is penetrated by a number of 

 small tracheae given off from the chief trachea of the thorax. They 

 seem to be transformed longitudinal flight-muscles in process of atrophy. 

 They appear at the last moult at the same time as the wings and elytra, 

 and they show in the different types different degrees of degeneration. 

 Flight is occasional in Ranatra : it does not seem to have been observed 

 in Nepa ; it does not occur in Naucoris. 



* Arch. Zool. Exper.,liv. (1914) Notes et Revue, No. 3, pp. 58-73 (3 figs.)-. 

 + Rev. Suisse Zool., xxii. (1914) pp. 121 45 (2 pis.). 



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