PART I. EAR-SIZE. 



INTRODUCTION. 



The inheritance of ear-size in rabbits has been characterized as blend- 

 ing, in certain preliminary publications, (Castle, 105, :o$a). 1 The experi- 

 mental evidence for such a characterization is described in the following 

 pages. It consists of results obtained by experimental cross-breeding of 

 lop-eared rabbits with ordinary short-eared ones. A detailed account 

 of this evidence is of little interest to the general reader, who therefore 

 may advantageously omit pages 14-34. For consultation on the part of 

 the critical student of heredity, it has been thought essential to present this 

 evidence in some detail, even though it is intrinsically uninteresting. 



CHARACTERISTICS OF LOP-EARED RABBITS; STERILITY AND ITS 



INHERITANCE. 



Lop-eared rabbits are distinguished from ordinary ones chiefly by the 

 enormous size of their ears, which are so large as to hang down, touching 

 the ground on either side of the head. (See plate i, fig. 2, and plate 2, 

 fig. 8.) This breed of rabbit is characterized also by a long tail and 

 unusual size, being one of the largest breeds known. The characters of 

 large size and long tail, however, have probably not been sought for their 

 own sake, but have been incidentally obtained in the production of the 

 breed as a result of selection for ears of large size; for among lop-eared 

 rabbits, as a rule, those of the largest size have longest ears. 



In the winter of 1904 a pair of lop-eared rabbits was obtained from a 

 fancier and used in various breeding experiments. Matings of the two 

 together were for the most part fruitless, only one litter of 2 young being 

 successfully reared. These were similar to the parent rabbits in size and 

 ear-character. Of the two, one was a male, which was used extensively 

 in breeding experiments, including one successful mating with his mother, 

 from which came a good-sized litter. But only two out of this litter at- 

 tained the age of 20 weeks and they ultimately succumbed to disease under 

 conditions not unfavorable to other rabbits. The second of the two young 

 reared by the original lop-eared pair was a female. Only twice did this 

 rabbit bear young by any sort of mating. In one case she failed to rear 

 any of the young. In the other case she reared, when mated to her own 



1 For complete titles see Bibliography, p. 69. 



