90 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



the tables, I mean, as stated above, that the epididymis was full of 

 motile sperm and showed very few or no other cells. Males showing 

 many motile sperm first occurred in the F3 or 5 wild generation. 

 Although no previous hybrid generations had shown motile sperm, 

 nevertheless, in this generation, 7 individuals showed a condition similar 

 to that of any mormal male guinea-pig. The percentages showing 

 many motile sperm increased from 14 per cent in the F3 to 73 per cent 

 in the F7 generation. 



THE RESULTS OF A COMBINED MICROSCOPIC AND BREEDING TEST. 



The results of the microscopic tests have been discussed. About 

 one-fourth of the animals tested in that way were also tested by breed- 

 ing. Of the 433 males tested microscopically, 102 also had a breeding 

 test (see table 76). The order of the test was not always the same, 

 for about two-fifths of these males were bred first and then subjected 

 to a microscopic test; but since the contents of the epididymis were 

 the same under varying conditions, it should have had no effect on 

 the results. For convenience, we may divide the animals into classes 

 somewhat similar to those used in discussing the miscrocopic tests. 



(1) Hybrid males without spermatozoa. — Twenty-three males of this 

 type had been mated to females before a microscopic test was made. 

 As was to be expected, none of them were fertile in breeding. 



(2) Hybrid males with immotile spermatozoa. — Eleven hybrids with im- 

 motile sperm proved sterile in breeding. The number of sperm varied 

 from a few in some cases to many or practically all sperm in others, 

 but since aU were immotile, they were, to be sure, completely sterile 

 in breeding. 



(3) Hybrid males with a few motile spermatozoa. — ^It is very difficult to 

 classify males with motile sperm, since all grades existed, ranging from 

 individuals with very few motile sperm to individuals with thousands 

 of them. In all microscopic tests animals were recorded with reference 

 to the number of sperm present and proportion of these that were 

 motile. The relative number of sperm was described as "few," "half," 

 "over half," and "all;" and the standard for "all" was the normal 

 guinea-pig male or a completely fertile hybrid male. For example, a 

 male recorded as "half" had sperm and the usual cells in about equal 

 numbers, or he might have none of the usual cells but a deficiency 

 of sperm. The motility was described in the records as "1," "2," 

 " 3," and "4." These signs had the following significance : " 1 " meant 

 a few of the sperm present were motile; "2" meant half of the 

 sperm present were motile; "3" meant over haK of the sperm present 

 were motile; "4" meant that all of the sperm present were motile. 

 Obviously, this divided continuous variates into 16 crude classes. A 

 male recorded as "half 4" had about half the usual number of sperm, 



