ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 165 



thicker. Their best development is dorsally, close to the lens. Only in 

 Gigantura is there on the ventral wall, about the middle, a small repre- 

 sentation of the accessory retina. The; eyes are directed not laterally but 

 dorsally, or rostrally ; and the interorbital space is reduced to such a thin 

 septum that the eyes almost touch, like the eyes of one looking through 

 a field-glass. While many of the eye-muscles are divergent or reduced, 

 when compared with the norm, the accommodation-apparatus is well 

 developed. The author gives many detailed illustrations and a general 

 interpretation of these peculiar eyes as adaptive to special conditions. 



c. General. 



Biological Observations on Reptiles and Amphibians.* — F. Werner 

 gives in the first place an account of his experiments as to the " tropisms " 

 of reptiles and amphibians, (a) Most reptiles are more or less markedly 

 heliotropic, and many seek the light apart from warmth. In amphibians, 

 heliotropism is much less marked, (b) The persistent upward climbing 

 of species of Hyla, Dryophis, Anolis, and Chamcdeon is interpreted as 

 negative geotropism. {c and d) Positive geotropism is always associated 

 with stereotropism, as seen in AmphisbasnidEe, Typhlopidas, Scincoidae, 

 and limbless amphibians, (e) Hydrotropism, as a particular kind of 

 ■ckemotropism, is strikingly illustrated by Triton, Bomoimtor, Ungalia 

 semicincta, Gerrhonotus cceruleus, &c, which persistently make for water, 

 even from considerable distances. 



Secondly, Werner discusses the sensory perceptions of reptiles and 

 amphibians (186 different forms). (1) Vision is particularly acute as 

 regards food and enemies. Crocodiles, which see best sideways, do not 

 seem to perceive a fish at a distance greater than half their own length, 

 but they see a man at ten times their own length or even more. Tor- 

 toises far excel crocodiles in acuteness of vision as regards food, but they 

 seem less sensitive to the approach of man. Some lizards can see food 

 at a distance of 1-3 yards ; others are very short-sighted. Snakes are 

 mostly dull of sight. The Urodela are far inferior to the Anura in range 

 of vision. A large number of precise measurements in terms of body- 

 length are given. (2) As regards hearing, all reptiles are deaf or at any 

 rate dull ; the crocodiles react to a few noises, and the geckos come next. 

 The Urodela have little power of hearing, but frogs have considerable 

 sensitiveness. (3) All the forms tried reacted to strong odours, such as 

 those of alcohol and formol. (4-6) Interesting facts are given in regard 

 to the gustatory, tactile, and pressure-senses. 



In his third chapter Werner discusses maximum and minimum size. 

 He notes that the attainment of maximum length does not coincide with 



1 1 



sexual maturity. Half -grown chaniaedeons, snakes, &c, may be sexually 

 mature. In many cases there is no definite limit of growth ; many grow 

 .as long as they live and never show any senile weakness, their death 

 being violent not " natural." Even in abnormally large individuals there 

 is no trace of senile degeneration. An interesting set of figures show 

 for Boa, &c, a ratio between the adult size and that of the newly-born 

 .young. Length of life is also discussed, and it is noteworthy that within 



* Biol. Centralbl., xxii. (1902) pp. 737-58. 



