THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 231 



100 

 90 

 80 



: 60 



^50 



40 

 30 

 20 

 10 



-FETAL WT.CL. 5 



- II II h 4 



_ II M il 3 



II II 2 



M II I, 1 



-UNIMPLANTED 

 PREG. 



-NOT PREGNANT 



M 



M J J A 

 MONTHS 



N 



Figure 91. — Phases in the reproductive cycle of the female sea otter as re- 

 vealed by ovary and fetal examinations of four samples of reproductive 

 tracts. Although some of the samples are small, they illustrate that large 

 fetuses and implanted pregnancies predominate in summer and that 

 pregnancy is at a maximum in late winter and spring. 



Conceptus size and development 



To compare the conceptuses that were recovered from reproduc- 

 tive tract samples, the embryos and fetuses were classified ac- 

 cording to five arbitrarily chosen weight classes following a 

 logarithmic scale (table 50). The conceptuses ranged in weight 

 from a fraction of a gram to 1,869 g. (4 lb.). When the weights of 

 fetuses taken in different seasons are compared, it is shown that 

 in winter conceptuses of small size predominate and in summer 

 large fetuses predominate. The series of photographs (figs. 92 and 

 93) illustrate stages of development. The comparative sizes of the 

 conceptuses in the samples from different seasons were useful in 

 indicating the timing of certain phases of the reproductive cycle 

 (see Chapman's analysis that follows). 



The morphology of the female reproductive tract was studied 



