446 SUMMARY OF CURRENT RESEARCHES RELATING TO 



with vascular spaces, and an inner layer of bony laminae, probably ossified 

 fibrous tissue of the cutis. The cosmoid scale grows in thickness only 

 by the addition of new lamellae below ; its outer surface is covered with 

 a thin shiny layer, the nature and origin of which are uncertain. 



3. The ganoid scale is found in all Actinopterygii except the modern 

 Teleostei. In its full development it is seen in the rhombic scales 

 of Palceoniscus and Lepidosteus. It grows in thickness by the addition 

 of new layers, not only below but also on the upper surface. The 

 oldest part of the scale is the centre. The lower layers are bony or 

 fibrous, the upper of much denser homogeneous enamel-like ganoine. 

 The palaeoniscoid and lepidosteoid scales are two distinct varieties of 

 the ganoid scale. 



Besides cosmoid, palaeoniscoid, and lepidosteoid scales, certain other 

 varieties are found, such as the Rhizodont and Dipnoan, which are 

 probably to be derived from the cosmoid. The position of the 

 Coelacanth scale is at present difficult to determine ; it may be a primitive 

 form in which the denticles have uot yet fused to a cosmine layer, as 

 Williamson supposed ; or it may be simply a degenerate cosmoid scale 

 to the surface of which denticles have become attached. 



The cosmoid scale occurs in the extinct Osteolepidoti (Crossopterygii) 

 and Dipnoi, but in no other group of fish. Similarly, the ganoid 

 scale occurs in the Teleostomi and never elsewhere. The palaeoniscoid 

 type is restricted to the Palaeoniscidae and their immediate allies ; while 

 the lepidosteoid type is universal among the Protospondyli, the iEtheo- 

 spondyli and the Pholidophoridae, and not found in any other group 

 as far as is known. 



The scale of Polypterus is of the ganoid type and belongs to the 

 palaeoniscoid variety. The scales of Acanthodii are not placoid, but 

 approach most nearly to the lepidosteoid type. 



Seasonal Change in Birds.* — C. W. Beebe publishes a pre- 

 liminary report of some experiments on birds, undertaken with a view 

 to finding out what factors determine the seasonal changes in the 

 plumage of male birds. The tanager (Piranga erythromelas) and the 

 bobolink (Dolichonyx oryzivorus), in which the summer and winter 

 plumage are markedly different, were the subjects of these experiments, 

 which dealt mainly with one factor — the condition of the bird as to 

 fatness or thinness. Males in full nuptial plumage, which had not been 

 allowed to breed, were kept in small cages in a dim light, and fed rather 

 more abundantly than usual. They soon became less active, ceased to 

 sing, and increased in weight. In autumn no trace of the usual moult 

 could be discovered, and the birds remained in perfect health. A few 

 were taken into the light, and their diet changed, and they soon began 

 to sing. A sudden alteration of temperature either upwards or down- 

 wards wrought a radical change. They stopped feeding, lost weight, 

 and rapidly moulted into the normal winter plumage. Those that were 

 kept the whole time in dim light with high feeding were gradually 

 brought into normal conditions in spring, and very quickly they began 

 to moult into new nuptial plumage, having skipped the winter stage 



* Amer. Naturalist, xlii. (1908) pp. 34-8. 



