Publisher's Synopsis
Excerpt from Heredity of Hair-Length in Guinea-Pigs and Its Bearing on the Theory of Pure Gametes, And, the Origin of a Polydactylous Race of Guinea-Pigs
A litter of four guinea - pigs of a pure short-haired race yielded measure ments which combined are expressed graphically in Fig. 2, A. Starting at birth with a length of about 18 mm., the hairs grew very rapidly during the first week, at the end of which they measured about 25 mm., an average increase of a millimeter a day in the second and third weeks they grew less rapidly, measuring about 29 mm. At the end of two weeks, and 33 mm. At the end of three weeks. At this time the growth of the hairs which the animals bore at birth was practically complete; the hair-follicles now ceased to form medullary substance, and consequently the hair narrowed to a base of solid cortex (fig. I). From this time on the measurements Show from week to week only slight deviations from a length of 3 3 to 3 5 mm.
Several series of measurements of the hair of long-haired guinea-pigs, when combined and expressed graphically, are shown in D, Fig. 2. The hair-length at birth is about the same as in animals of class A, or even a little shorter, but the growth rate does not show the series of rapid changes seen in class A. Growth progresses very steadily at an average rate of about min. A day during the first one hundred days and at about mm. A day during the second one hundred days. But a glance at Fig. 2, D, shows that the slowing up of the growth rate is a very gradual process.
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