212 Arthur Willey, 



has to be acconimodated to the general situs viscerum. In order 

 to appreciate this point of space-relations, it would be useful to 

 compile a table to show the ratios between the size and number 

 of the mature foetns and the size of the parents in different cases. 

 In the case of the beaver described in this paper, the crown-rump 

 measurement of the foetus was abont 130 mm; the trunk-measure- 

 ment (snont to vent) of the parent was 27 inches or about 680 mm. 

 The proportion is therefore 13 : 68 or about 1 to 5. 



Unilateral gestation necessarily occurs in all species of mammals 

 which normalty give birth to one oifspring at a time. even when the 

 foetus is lodged in a median Uterus simplex. It is not common 

 to find pluriparous mammals carrying their young at a given mo- 

 ment in one hörn only of the Uterus. 



In Sir William Turner's description of the placentation of 

 Macacus cynomolgus (1878) he remarked that the right ovaiy 

 was purplish coloured and contained a corpus luteum; the left 

 ovary was cream-coloured with numerous semi-transparent specks 

 on its surface. The foetus was a male, covered with hair. 



On the other hand difterent results were obtained by Sir 

 William Türner in the case of Lemurs. A gravid Uterus of 

 Propithecus diadema contained a single foetus which occupied 

 the corpus uteri and left cornu. The right ovary was about the 

 size of a common pea; the left was double the size, and contained a 

 corpus luteum. The foetus was well developed, and measured 5 

 inches from the tip of the nose to the root of the tail. The tail 

 was 3% inches long. The surface of the body was covered with 

 hair, and the nails were distinct. The incisor, canine, and premolar 

 teeth were erupted, but the molars were concealed by the gum. 

 The foetus was a male. In this instance therefore the foetus was 

 sinistral and male. A somewhat larger sinistral foetus of Lemur 

 rufipes was not sexed. Of four specimens of the gravid uterus of 

 this species (L. rufipes), the corpus luteum was found in the 

 ovary corresponding to the gravid cornu in three instances; in the 

 fourth it was in the ovary of the opposite hörn (Turner 1876). 



The Canada Porcupine is a highly specialised Eodent of seini- 

 arboreal and solitary habits. According to C. H. Merriam (quoted 

 by Seton) the young are born about the first of May and are 

 monstrous for the size of the species. They are actually larger, and 

 relatively more than 30 times larger, than the young of the Black- 

 bear at birth. On May 1, 1882, at Big Moose Lake, Merriam „shot 



