ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 939 



The frequent statement that " after the full development of the 

 feather, the calamus is constricted, and the cutis papilla dies," is 

 denied, since the calamus is never wholly constricted, and before the 

 feather is half-grown the upper portion of the papilla is dead. The 

 throwing off of the " epitrichium " layer, and of the horny sheath from 

 the stratum corneum superius is then described. 



The process by which the outer and medullary cells undergo 

 horny change, the origin of the pigment from wandering cutis cells 

 and independently within the outer cells of the radii, the different 

 forms and distribution of permanent feathers, the phenomena of 

 moulting, the homologies of scales, feathers and hairs, and lastly the 

 historic evolution are briefly discussed. 



Monstrosities in the Egg of the Chick.* — M. C. Dareste has made 

 a number of fresh observations on the production of monstrosities in 

 the egg of the chick by a modification of the germ previous to 

 incubation. He finds that eggs put to incubate four days after laying 

 gave no monsters; of eight eggs he found that of those put to 

 incubate after five days two, of those put after six days one, and of 

 those put seven days after, three produced monsters. He comes to 

 the conclusion that the diminution of the vitality of the germ, which 

 determines the teratological evolution, may be, at least at elevated 

 temperatures, very precocious; as normal and monstrous embryos 

 were found side by side, it is not the incubatory process that is at 

 fault, there must be some modification of the germ anterior to incuba- 

 tion. This can only be explained by a reference to that individuality 

 which, as the author has long since shown, plays so great a part in 

 teratogeny. What these anterior modifications are we cannot now say, 

 for we only know them by the result of their influence on the embryo. 



Influence of Gravity on the Frog" Ovum.-f— In reporting Prof. 

 G. Born's recent researches on hybridization, a brief review may 

 be given in the first place of his previous investigation as to the 

 influence of gravity on the frog ovum. Pfliiger had shown that ova 

 fixed in a given position when the gelatinous envelope was not com- 

 pletely swollen, retained this position both externally and internally. 

 This method was utilized in order to investigate what happened 

 when definite regions were placed uppermost. If the clear region 

 was directed upwards, and it is known from the way the egg floats, &c, 

 to contain the heavier material, a readjustment took place. Tho 

 specifically heavier albuminous substance slid downwards, the lighter 

 was gradually forced to the top. So it happens within the mother in 

 the ova fixed with the clear region uppermost. The process is com- 

 plicated, however, by a number of factors : — the superficial layers are 

 firmer than the more fluid interior ; the interior matter is emulsion- 

 like and viscid, not mixing readily with the rest, so that in movement 

 sharp bounding layers are formed ; and finally the whole sphere is 

 influenced by the pressure of the imperfectly swollen gelatinous 

 envelope." 



* Comptes Kendus, ciii. (18S6) pp. 355-6. 



t Arch. f. Mikr. Anat., xxiv. (1885) pp. 475-545 (2 pis.). 



