Section III.—Early Development of the scales.

The early development of the scale was studied in a series of hatchery-reared brown trout fry. The material consisted of 155 specimens of Salmo trutta. They ranged in length from 2.0 cm. to 8.0 cm. The eggs from which they were hatched were obtained during June, 1930, from fish stripped in the Lower Selwyn River. They hatched during the spring of 1930, and fortnightly samples were taken during December, 1930, January, February, and March, 1932.

The fry were preserved and treated for scale observations by the method given by Paget (1920). From specimens preserved in 5% formaldehyde, one-half (the right side) of the skin (epidermis and dermal layers) was removed in one piece and stained with haematoxylin. The results, as Paget also found, were very satisfactory, especially when the fish were placed in weak (30%) alcohol for a day or two previously to staining. In this way the epidermis was removed, thus giving a clear view of the dermal tissues in which the scales are developed.

My results, which agree substantially with those of Paget (1920), may be summarised as follows:—

The scale papillae were first observed along the lateral line, slightly posterior to the dorsal fin, when specimens were from 2.4 cm. to 2.8 cm. in length (see Fig. No. 1). From this area they gradually developed in an anterior and posterior direction along the lateral line, at the same time spreading dorsally and ventrally, until eventually the whole surface was covered. They tended to spread more quickly dorsally than ventrally. In several instances of fish ranging from 3.8 to 6.0 cm., fully formed scales with one to four circuli were found above the lateral line, and slightly posterior to the middle of the body, while those on the belly and immediately