. Chemical embryology. Embryology. SECT. 6] OF THE EMBRYO 873 Erithracus rubecula cently extended it to the eggs of many other birds, mostly wild species. Their data are fragmentary, and not suitable for compression, but in all cases they found that the larger the embryo, the less was its water-content. They also found a falling weight of the whole egg during development, four ex- amples of which are given in Fig. 222. The amount of weight lost by eggs of various birds dif- fered, but never exceeds 30 per cent of the original weight. Table loi gives these differences concisely. For a given bir
. Chemical embryology. Embryology. SECT. 6] OF THE EMBRYO 873 Erithracus rubecula cently extended it to the eggs of many other birds, mostly wild species. Their data are fragmentary, and not suitable for compression, but in all cases they found that the larger the embryo, the less was its water-content. They also found a falling weight of the whole egg during development, four ex- amples of which are given in Fig. 222. The amount of weight lost by eggs of various birds dif- fered, but never exceeds 30 per cent of the original weight. Table loi gives these differences concisely. For a given bird, such as the hen, the loss is so constant that Zunz suggested frequent. Fig. 222. weighing as a guide to regulation of normal development. It is interesting to recall that other terrestrial eggs, the silkworm (Luciani & Piutti) lose water as they develop. Table 101. Loss of weight by fertile eggs during incubation. Species Hen (Callus domesticus) Hen( „ „ ) Hawk {Buteo buteo) ... Falcon {Cerchneis tinnunculus) Pheasant [Phasianus colchicus) Nightingale {Turdusphilomelos) Yellow-hammer {Emberiza citrinella sylvestris) Chaffinch {Fringilla coelebs) Linnet {Acanthis cannabina) Robin {Erithracus rubecula) Sparrow {Prunella modularis) ... Warbler {Sylvia communis) ... ... Starling This progressive water loss is one of the main difficulties in the way of successful in vitro incubation of the avian embryo, a technical problem which has not yet been solved; see Loisel (2 or 3 days), Vogelaar & Boogert (6 days), Fere; McWhorter & Whipple and S. Paton. % Investigator 17-9 14-9 11-5 Tangl Murray Groebbels & Mobert 23-0 II-8 26-8 12-2 IPs 17-0 12-55 Tangl Iljin and Alcacid working with different incubators, some using wet air and others dry, observed a greater loss of weight in the latter, but the most complete examination of evaporation-rate is that of Murray. His immediate aim was to find the optimum conditions for 56-2 -. Please note that these images are
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