66 WALTEH HEAFE, 



I am tempted to suggest the probability that there is 

 preseiit in the blood from time to time what may be called 

 an CBstrus toxin^ to suggest that its presence is due to the 

 external and internal forces mentioned above, and to relegate 

 to it the power which stimulates the activity of the sexual 

 season, and brings about the actual production of those 

 generative elements which nutrition has enabled the animal 

 to elaborate. 



It appears to me that research in this direction would be 

 likely to be rewarded ; it would not only be of great theo- 

 retical interest, but might well lead to increase of knowledge 

 regarding some of the causes of sterility, and prove of enor- 

 mous practical value. 



Literature. 



Allen. — " The Americaa Bisons, Living and Extinct," ' Mems. of Museum 



of Conip. Zool. at Harvard Coll., Cambridge, Mass.,' 1876. 

 Altmann. — Article in ' Jaliresbericlit iiber die i''ortsch. der Auat. und 



Physiologic,' Hoffmann and Schwalbe, vol. vi, 1878. 

 Aristotle. — ' History of Animals,' Eohn's Library, 1883. 

 Beakd. — ' The Space of Gestation and the Cause of Birth,' Jena, 1897. 

 Beevee. — •' Notes on Eields and Cattle,' 1870. 

 Bell. — 'A History of British Quadrupeds,' 2iid edit., 1874. 

 Benecke. — " IJ eber Keif ung und Befruchtuiig der Lies bei den Elcdermausen," 



' Zoologischer Auzeiger,' vol. ii, 1879. 

 Beneden and Julin. — "Observations sur la maturation, la fecondation, et la 



segmentation de I'oeuf chcz les Cheiroplercs," ' Archives de Biologic,' 



vol. i, 1880. 



BiscHOFF. — ' Entwicklungsgeschichte des Rehes,' Giesscn, 1854. 

 BiscHOFF. — " Ueber die llanzzeit des Euchses und die erste Entwicklung 



seines Eies," ' Sitz. der Math.-phys. Classe vom 13 Juni, vol. ii, 



1863. 



Bonnet. — Articles in ' Deutsche Zeitsclirift fiir Thiermedicin,' vol. vi, 1880 

 vol. vii, 1882. 



Bonnet. — Article in Ellenberger's ' Vergleichende Pliysiologie der Haussau- 

 geihiere,' 1892. 



