8 



SPERM FORMATION 



spermatozoa (Fig. 11) are formed and the 

 hybrid remains sterile. 



"There are no authentic cases on record 

 showing that fertility ever occurs in this hy- 

 brid." 



Shortly after Wodsedalek uttered these 

 sweeping conclusions, Lloyd-Jones of Iowa 

 State College cites (Jour, of Heredity., Nov., 

 1916) a number of cases from literature in 

 which female mules and "hinnies" were un- 

 questionably the mothers of colts. The most 

 authentic case cited was that of a hinny 

 owned by Mr. J. M. Bryant, of Quincy, Ind. 

 This hinny was reported as having been in 

 foal three times. The first two colts were 

 deformed and died, but the last pregnancy 

 resulted in normal twins. Another interesting 

 case is reported by Dr. D. W. Sullivan, of 

 Weed, Cal. This animal is out of a standard 

 bred mare by a mammoth jack. She was put 

 to a black Percheron stallion and produced 

 a male "grade mule." 



I have been unable to find any record either 

 authentic or otherwise of a reproducing male 

 mule. It is true that the test is less likely 

 to be made with the male mule, as practically 

 all are castrated when yearlings and they do 

 not reach sexual maturity until about two 

 years old. 



When such contradictory cases as those 

 just cited are brought to light, the cytologist 

 can only become more conservative and seek 

 an explanation for the exceptions. In the 

 first place, we could easily assume with Lloyd- 

 Jones that the maturation of germ cells of 

 the female were sufficiently different to permit 



an occasional complete development of an 

 ova, but never of a spermatozoon. To one 

 who has made a comparative study of the 

 development of the germ cells of the two 

 sexes, this assumption does not seem justifia- 

 ble, especially in the present case, where the 

 number of chromosomes of the parents dif- 

 fers so greatly. In fact, it seems just as 

 possible for a male mule to reproduce as a 

 female, the chances of course, being greater 

 for the latter to be put to test. 



In a study of hybrid pheasants it was found 

 that most maturing cells were destroyed about 

 the time of the first maturation division (Fig. 

 7). However, some continued their normal 

 development through the second division 

 (Figs. 8 and 9), and still others formed ab- 

 normal sperms (Fig. 11, fourth sperm). 

 Since the same condition, though less marked, 

 was found in the hybrid pigeons, and the 

 mule, it seems evident that the point of de- 

 struction depends entirely upon chance. This 

 being the situation, it seems quite plausible 

 to assume that in rare instances a chromoso- 

 mial arrangement might be brought about by 

 which a certain number of maternal and pat- 

 ernal chromosomes are paired, those having 

 no mate either continuing unpaired or being 

 extruded from the cell. Much more light 

 will be thrown upon this subject when material 

 for the study of the germ cells of the ass 

 can be obtained. Regardless of the accuracy 

 of these or any other technical assumptions, 

 we are forced to -jigree if the a bove cases aj ;e 

 to be accepted, that the production ot ott- 

 spring by the common mule is indeed a reality. 



