400 CHARLES I;. STOCKARD AND E. M. VICARI 



failing to whelp at all or giving litters of only one to three 

 puppies. In contrast, closely related individuals may pro- 

 duce from ten to seventeen puppies at a whelp. One such 

 hitch in our colony produced fifty puppies within two years, 

 while five of her highly typed relatives were perfectly useless 

 hreeders throughout their lives. The achondroplasic bulldog 

 types produce only small litters, rarely more than four or 

 five puppies, and often only one or two, while the normal 

 typed dog produces from six to eight puppies at a time. 

 First generation hybrids derived from crosses between types 

 with distorted fecundity and the normal type are all fairly 

 productive, while individuals of the second hybrid genera- 

 tion often show great irregularity in fecundity and some 

 may be entirely sterile, as is not uncommon among the F 2 

 bulldog-bassethound hybrids. The entire question of the num- 

 ber of offspring to be produced at one litter is probably 

 analyzable on the basis of the wide differences in litter size 

 found among the different dog types. 



Various deviations from the usual pattern of the normal 

 canine are also presented by such breeds with abnormal 

 endocrine glands. There are considerable differences in sus- 

 ceptibility to gross parasites as well as differences in re- 

 sistance to infectious diseases. Such facts have emphasized 

 the importance of a careful survey of the glandular char- 

 acteristics among the different breeds in order to follow the 

 inheritance of these characters in their hybrids. The corre- 

 lations between the glandular deviations and the physical 

 characters of the individuals in hybrid generations are of 

 primary importance to the problem of constitutional and 

 functional modifications. 



Our attention lias been centered mainly upon the more 

 important of the endocrine glands — the pituitary, thyroid, 

 parathyroids, suprarenals and gonads, with observations on 

 the size and condition of the thymus. Glands from the pure 

 breeds and hybrids have been systematically observed and 

 studied in the fresh condition at autopsy and subsequently 

 as fixed preparations. 



