ZOOLOGY AND BOTANY, MICROSCOPY, ETC. " 61 



consists of a peripheral condensation or massing of the reticulum. There 

 is a similar but thinner perinuclear condensation of the reticulum 

 bounding the confines of the nucleus, and forming a nuclear membrane 

 in the nucleated forms. The central nuclear knots of the mammalian 

 red blood corpuscles represent remains of the nuclear membrane and 

 reticulum originally existing in the central part, and result from or 

 after the disturbance of the interior produced by disintegration or 

 extrusion of the nucleus. 



Silvery Colour of Fishes.* — P. Murisier supports Popoflf's view 

 that the silvery sheen of open-water fishes is protective, since it 

 harmonizes with the surface, which appears silvery when seen from a 

 certain depth. The silveriness of the surface is due to the fact that the 

 oblique rays of light which penetrate into the water undergo a double 

 total reflection — the first from below upwards in meeting fine particles 

 in suspension, the second from above downwards at the bounding sur- 

 face between the water and the air. The silvery appearance of the 

 ventral surface of fishes makes tliem invisible to carnivorous enemies 

 looking up from below. Fishes of deep and dark waters tend to be 

 sombre. 



Murisier has experimented with lake-trout {Trutta lacustris), and 

 finds that if these are reared for nine months in bright light on a white 

 floor, the ventral surface and the sides are brilliantly silvery ; while if 

 they are reared in darkness, or on a dark-coloured floor, they are sombre 

 and without silveriness. The melanophores normally form a screen 

 absorbing the light-rays : if the screen is not developed, or is inter- 

 rupted, then silveriness is produced. The non-development of the 

 melanophores is due to a nervous influence operating through the eyes. 

 Blind trout remain of a dull colour on a white ground. The adaptive- 

 ness of the silvery colour is thus very direct. 



c. General. 



Diseases of Fishes-j — T. Southwell reports on a variety of diseases 

 in Indian fishes. The subcutaneous intermuscular tissue of Rasbora 

 daniconius ( = Cyprinus dankonius) was found in four cases infected 

 with Myxosporidia, probably of the genus Mijxoholus, and closely allied 

 to Glugea homhycis, which causes silkworm disease. In the skin of 

 Cirrhina lata were found cysts with cercarise, possibly the young of 

 Holostomum cutkola ; other cysts with cercarise were found in the skin 

 of Nuria danrica and in the superficial muscles of two other fishes. A 

 carcinoma of the thyroid of the rainbow trout (Salmo irideus) is de- 

 scribed. A new parasitic Isopod {Rocinella latis sp. n.) was found on 

 Lates calcarifer, the Bhekti, Argidus foUaceus from the skin of Laheo 

 rohita. From the ccelom of Diagramma crassisplnum were obtained 

 specimens of Amphilina magna sp. n. The transparent flesh of the 

 "• Bombay duck," Harpodon mhereas, contained cysts of the larvte of 



* Proc. Verb. Soc. Vaud. Sci. Nat. (1915) pp. 95-7, in Bull. Soc. Vaud., 1. (1915). 

 + Records Indian Museum, xi. (1915) pp. 311-30 (3 pis.). 



