544 SUMMARY OF CURRENT RESEARCHES RELATING TO 



which the organ opens into the anterior part of the lower portion of the 

 nasal cavity, the resemblance is much closer to the mammalian con- 

 dition than to the lacertilian, and in general it may be said that its 

 condition in Sphenodon affords additional evidence, if such be required, 

 of the reptilian affinities of the mammalia. 



Multiple Testis and Liver.* — H. Gerhartz gives particulars of 

 two cases of Rana fusca where, in addition to the normal testes, 

 accessory glands were present showing sex-cells in normal development. 

 One of the frogs further showed two minute sago-like structures 

 attached to a vein in the body cavity. These were found to possess a 

 liver structure, with cells apparently in an active condition. 



Coloration of Fishes.f — M. Popoff discusses the discoloration of fishes, 

 with especial reference to its interpretation in terms of the formula of 

 natural selection. Almost all fishes are silvery below, and darker above, 

 but there are exceptions. In those living in large rivers, ponds, and 

 seas that are not very clear, the silver of the under-surface is often 

 partially hidden by a dull yellow veil ; in Salmonidae, some of which 

 feed chiefly at night, or habitually hide under stones and water plants, 

 the colour is often brown, or red or dark ; in most deep-sea fishes there 

 is usually a dull colour over the whole body. 



The silvery coloration is usually associated with clear water. Mandoul 

 has interpreted the silver shimmer as due to pigments of the uric series, 

 to which guanin belongs, and has correlated its prevalence with defec- 

 tive renal organs. But this interpretation by itself is far too general. 

 Thayer's suggestion as to the protective advantage, well seen in some 

 birds, of having a lighter groundwork on the under-surface is then 

 considered, but Popoff finds that it is not generally applicable. When 

 the visual arrangements and powers of fishes are considered, it becomes 

 evident that a lighter coloration on the under-surface will not protect 

 fish against fish. Moreover, the under-surface is not merely light, it 

 is silvery. A careful consideration of the conditions of illumination in 

 the water leads, however, to the conclusion that the silvery under- 

 surface seen against the silvery surface of the water is of great protective 

 value. The author discusses various types of coloration which may be 

 interpreted as in harmony with different conditions in the transparency 

 and illumination of the water. He gives particular attention to the 

 Clupeidae, the Salmonidse, the Percida?, the Gadidas, and the deep-sea 

 fishes. Of particular interest are cases where different species of the 

 same genus have different coloration in correspondence with their 

 different habits. Thus Bhnnius rouxi, which lives in the clear sea- 

 water, is very silvery, while B. cagnotha, which lives in not very clear 

 fresh-water, has a yellowish tint ventrally. Popoff's general conclusion 

 is that the silveriness of the under-surface in fishes is a subtly-developed 

 protective adaptation. 



Spiracular Organ in Lepidosiren and Protopterus4 — W. E. Agar 

 gives some particulars regarding a tubular organ " enclosed in a hoop 

 of cartilage springing from the lateral wall of the auditory capsule." A 



* Anat. Anzeig., xxviii. (1906) pp. 522-8. 



t Biol. Centralbl., xxvi. (1906) pp. 272-82. 



X Anat. Anzeig., xxviii. (1906) pp. 298-304 (5 figs.). 



