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NORTH AMERICAN FAUNA 74 



abundantly evident. Although many of the details of the actual search and 

 ingestion process will remain obscure until the animals can be closely observed 

 under natural conditions, the important factors now appear to be the strong, 

 sensitive snout and oral suction, rather than the eyes, tusks, and crushing teeth. 

 The tusks appear to function mainly as social display organs and weapons; the 

 function of the cheek teeth, if not in alimentation, remains unclear. 



Reproduction 



Reviewing the earlier recorded knowledge of reproduction in walruses, Allen 

 (1880) recognized that the female breeds at intervals of 2 to 3 years, gestation 

 lasts about 1 year, and a single calf is born in the spring and suckled for 1 to 

 2 years. Much additional information on this subject was contributed in the first 

 half of the 20th century by Chapskii (1936), Belopol'skii (1939), and Freiman 

 (1941), and in the second half by Brooks (1954), Mansfield (1958fl), Popov 

 (1960fl), Burns (1965), Krylov (1962, 1966Z?, 1966c, 1967, 1969), and Gol'tsev 

 (1975, 1978). These later studies were contemporary with mine and were 

 developed along similar lines. My principal objectives were to describe the 

 annual cycle of reproductive events and to relate age and physical development 

 to reproductive performance. 



I examined both males and females. For the males each testis was weighed to 

 the nearest gram, with and without epididymis, and measured in length and 

 width to the nearest millimeter. Immediately thereafter, a 2 x 10 x 10 mm 

 sample from the body of each testis and a similar slice from the mid-body of the 

 epididymis were fixed in AFA or 10 % formalin. These tissues were dehydrated in 

 ethanol, embedded in paraffin, serially sectioned at 7-10 /xm, stained in hema- 

 toxylin-eosin, and mounted on glass slides in Permount for microscopic 

 examination. For each specimen, the seminiferous tubules and epididymal ducts 

 were measured in 10 cross-sectional diameters taken at random. Histological 

 conditions in the tubules and ducts were interpreted principally on the basis of 

 Leblond and Clermont (1952), Ortavant (1959), and Roosen-Runge (1962). 



The uterus of each female was examined in the field within a few hours after 

 acquisition, at which time the ovaries were excised and fixed whole in 10% 

 formalin for later examination in the laboratory. The length and diameter of 

 each horn were measured, and the uterus was split open entirely and searched 

 for embryos and for endometrial lesions (placental scars) at the site of previous 

 placental attachment. The width, position, and color of each placental scar were 

 recorded, and the age of the scar from parturition to collection of the specimen 

 was estimated on the basis that: (1) the placental scar in animals known to have 

 given birth less than 24 h earlier was about 15 to 25 cm wide and was very rough 

 and bloody; (2) in females with calves estimated to have been 3 to 4 weeks old 

 (based on comparison with calves held in captivity), the healed scar was about 

 4 cm wide and deep reddish brown; (3) in females 6 months postpartum, the 

 placental scar was dark brown and about 3.5 cm wide; (4) 1 year after parturi- 

 tion, the scar was orange-brown and 3 to 3.5 cm wide; (5) after 2 years, the scar 

 was yellow-orange and about 2.5 cm wide; and (6) after 3 years it was pale 

 yellow and about 2 cm wide. Occasionally, I found an indistinct yellowish scar, 

 1 to 1.5 cm wide, that I judged to have been at least 4 years old. 



