PERIOD OF GESTATION. 47 



gestation were uniformly 360 or even 350 days, since the 2-y ear-old females do not 

 make their appearance on the rookeries until the last part of July, it would finally 

 come to pass that all the young would be born late in July, which is not the case. 

 The known facts are that the majority of pups are born between July 1 and July 15, 

 but quite a number of births take place after that date, occasional births occurring up 

 to September 1. A small, black pup was, however, killed on Kitovi, on October 16, 

 which was in good condition and weighed only 14^ pounds. This could, at the most, 

 have been only a month old, very likely not even that, and must have been born in 

 September. A large number of these small, late pups were seen on the various rook- 

 eries in October, so that scattering births certainly occur as late as the first week in 

 September. On account of these late births, and the date at which the 2 year-old 

 virgin cows make their appearance on the rookeries, there can be little doubt that the 

 first period of gestation is shorter than the succeeding ones. Were this not so we 

 would find a larger percentage of births late in the season, and it would be impossible 

 t.0 account for the retrogression of births toward the early part of June and July. Mr. 

 Clark, who has devoted some time to this question, writes as follows : 



The height of the season falls about the 10th or 15th of July, and it is reasonable to suppose that 

 the number of cows then visible and the increased number of births about that time are due to the 

 influx of the 3-year-old cows which come to bring forth their first young. These 3-year-old cows were 

 impregnated about August 1 of the preceding year. If we suppose that the first period of gestation is 

 350 days, this would bring the time of delivery about July 15. If the interval between delivery and 

 impregnation is about five days, the period of gestation remaining the same, the second birth would 

 fall about July 5, the third June 25, the fourth June 15, the fifth June 5, which is impossible, or at 

 least a sixth would be, for no births are recorded before June 10. 



If, however, we consider the second and succeeding periods of gestation to be about 355 days, the 

 interval between birth and impregnation remaining the same, the births would fall as follows : Second, 

 July 10; third, July 5; fourth, July 1; fifth, June 25, etc., the eighth falling on June 10. The cow 

 would then be 10 years old, probably still in bearing condition ; but there is every reason to suppose 

 that the period of interval between delivery and impregnation is less than five days. This figure, as 

 well as the one representing the period of gestation, has simply been taken arbitrarily for purposes of 

 illustration. With shorter intervals, say of three or even two days, the number of births necessary to 

 cover the interval in which births can occur would be increased. 



This is purely a theoretical discussion of this matter. The data regarding the period of gestation 

 and the interval between delivery and impregnation are wanting, and it would require several 

 seasons of xjainstaking observations to supply them. 6ut we have definite information regarding the 

 time at which the virgins are first served. We also know that the great mass of pups are born before 

 or about the middle of July, and we know that pups are born as early as June 10 to 12. That a 

 cow which was originally impregnated about August 1 can eventually bring forth a pup in early June 

 can only be accounted for by supposing a retrogression of the time of birth, for it must be the oldest 

 cows that bear their pups in early June. 



In order to definitely settle the matter careful observations of the younger cows 

 are needed, although the investigation is fraught with much difficulty. 

 Mr. Clark, who witnessed the birth of several pups, writes: 



In bringing forth her young the cow seems to take no thought as to her place. One pup was 

 observed to be born on a slanting rock down which it slipped as soon as released. The mother 

 reached down and lifted it up to her side only to have it slide down again. She repeatedly lifted the 

 pup back, and finally changed her position. Another cow was seen with her new-boru pup on a 

 narrow shelf which was scarcely large enough for herself, and from which the pair were in constant 

 danger of falling off. The pup must have been born there, but how is a mystery. 



The pup is born with the head first, though one birth was this season witnessed on St. Paul 

 where the hind flippers came first. Delivery seems easy. The cow shows but little evidence of pain, 

 though before delivery she shows more or less uneasiness, changing her position frequently, getting 



