ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 35 



•stage, the epithelial primordium forming an ellipsoidal body attached 

 to the epidermis by a constricted neck. The formation of the primary 

 -duct, the secondary, tertiary, and quaternary ducts, the epithelial hood, 

 and the mammary pit are described. The primordium of the nipple 

 was first observed on the twentieth day as a papilla at the bottom of the 

 mammary pit. The lumina of the ducts were first observed on the 

 eighteenth day ; they do not reach their definitive stage in the foetus. 

 They are apparently formed by re-arrangement of the cells. In the 

 •■earliest stages studied the mesenchymal cells are condensed around the 

 gland primordium ; they subsequently elongate and develop long fibrous 

 processes ; at twenty days and six hours these cells and fibres form the 

 greater part of the gland stroma, which includes (1) the thin mantle 

 layer immediately surrounding the ducts, and (2) the true stroma 

 between the ducts and outside of the mantle layer. The true stroma 

 contains the larger blood-vessels and nerves of the glands. 



Mammary Glands of Rabbit.* — J. Hammond finds that the de- 

 velopment of the mammary gland of the rabbit during the second half 

 of pregnancy is under the same influence as that which controls the 

 development during the first half — namely, the corpus luteum. Contrary 

 to the generally accepted opinion, the corpus luteum is active during the 

 :second half of pregnancy. The further development of the corpus 

 luteum, which takes place during the latter part of pregnancy, is due to 

 the influence of- the foetus. Hammond's experiments do not uphold the 

 view of Ancel and Bouin that the glandular phase of the mammary 

 gland is due to something entirely different from that which causes 

 the growth-changes, but confirm the views previously expressed by 

 Hammond and Marshall, that milk-secretion in pseudo-pregnancy 

 takes place in correlation with the involution of the corpus luteum. 

 Apparently the secretion of milk results whenever the influence causing 

 the glandular growth (the corpus luteum) is removed or lessened in 

 amount, provided that the initial development has gone far enough. 



(Estrous Cycle in Guinea-pig.t — Charles R. Stockard and George 

 N. Papanicolaou have shown that a typical oestrous cycle occurs in this 

 much-studied animal, and have followed the histological and physiological 

 •changes. The terminology proposed by Heape is used : — anoestrum, 

 period of rest in the female ; pro-oestrum, the first part of the sexual 

 season ; oestrum, especial period of desire in the female ; metoestrum, 

 the short period when the activity of the generative system subsides, and 

 the normal condition is resumed in case conception did not occur; 

 dioestrum, the short period of rest which in some mammals lasts only 

 a few days. The cycle in the guinea-pig, consisting of the four periods 

 — pro-oestrum, oestrum, metoestrum, and dioestrum — is known as »■ 

 dioestrous cycle. 



The regular dioestrous cycle repeats itself in non-pregnant females 

 about every sixteen days throughout the entire year. During each 



* Proc. Roy. Soc, Series B, Ixxxix. (1917) pp. 534-46 (1 pi.). 

 t Amer. Journ. Anat., xxii. (1917) pp. 225-S2 (9 pis. and 1 fig.). 



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