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THE AMERICAN NATURALIST [Vol. XLIV 



We have spoken thus far mainly of the work of botanists, for 

 the reason that little or nothing has been accomplished by zoolo- 

 gists until recently, which throws light upon the problem of ste- 

 rility. It was known by Aristotle that species would cross and 

 that the offspring varied from the parents in vigor and in other 

 characters. If the etymologists inform us correctly, the word 

 leopard, compounded of Leo, lion, and I'anlos. panther, or tiger, 

 points to a belief among the Greeks, that the leopard was a 

 cross between the lion and tiger. The knowledge that captive 

 animals bred only rarely, many not at all, and that even when 

 mating occurred, the act was functionless and no offspring re- 

 sulted, although the animals were apparently normal, is nothing 

 of recent date. As to why offspring are not produced under 

 these conditions, we are wholly ignorant. No one has deter- 

 mined whether the male actually convoys the fertilizing fluid to 

 the female and if so. whether functional spermatozoa are present. 

 It is known that in some eases, confinement of wild animals 

 induces degeneration of the internal generative organs. Psychic 

 causes, too, are undoubtedly present, inhibiting the mating in- 

 stinct, but these factors are so subtile that they defy analysis. 

 The data are familiar to every keeper of zoological gardens, and 

 yet no attempt, to my knowledge, has been made to determine 

 any of the details involved. 



Several cytologists have examined the gonads of hybrid animals 

 with a view to determining the condition of the sex cells. Thus, 

 Guyer studied the crossed pigeons from the cotes of Professor 

 C. 0. "Whitman at Chicago and found great abnormalities in the 

 secondary spermatocytes, such as clumping of the chromatin, 

 degeneracy of the cells as a whole, tri- and other abnormal mito- 

 ses. Spermatozoa were formed in many cases, but these cells 

 were obviously abnormal and pathologic. The gonads of the 

 mules obtained by crossing canaries and English goldfinches, 

 siskins, bullfinches, etc., are degenerate, and in some cases which 

 I have examined no trace of gonad could be found. 



The cytology of the gonad of the mule obtained by crossing the 

 mare with the jackass has been examined by H. E. Jordan who 

 describes the testis as follows : 



The seminiferous tubules are lined with Sertoli cells, spermatogonia 

 and a few primary spermatocytes in early stages. The nucleus of the 

 latter appears to be in the spireme phase of the contraction stage and 

 in process of regressive change. Mitoses are exceedingly rare and those 



