338 Journal of Comparative Neurology. 



March. This was after a week of warm rainy weather and the 

 ground had completely thawed out. These young averaged 

 42 mm. in length.^ A litter of four young just born were by 

 chance dug up on the 21st of March of another year. These 

 also averaged 42 mm. in length. I therefore conclude that 

 these two sets of young were of practically the same age. 



6 



Making use of Sutherland's (2) formula, T=M|/W, 

 to determine the period of gestation we can approximate the 

 time of mating. T is the gestation period in days. M is a 

 constant for the order or family. For Insectivora it equals 

 25. And W is the average weight of the adult in pounds. 

 The adult averages about .375 pounds. Hence we have 



6 



'p=:251 . 375, or T equals 21, the number of days of gestation. 



Mating then occurs early in February, at least a month 

 before the adults generally come to the surface. Two or three 

 males have been caught running over the snow early in Feb- 

 ruary which would indicate that this was a period of activity on 

 their part at least. Since one cannot locate accurately their 

 winter homes, it is practically impossible to catch the adult 

 females until they come to the surface in March, too late to get 

 the embryonic stages. Keeping the adults in confinement has 

 not met with success. Conditions for their normal activities 

 could not be easily provided, as they are rapacious feeders and 

 require a considerable range. 



The early stages of the development of the eye of the 

 European mole {Talpa eiiropaed) have been described by 

 Heape (3). He says that the beginning of the outfolding 

 which later forms the optic stalk is seen in an embryo 1.82 

 mm. long and at a time before the medullary groove has 

 closed at any point. They appear as two lateral depressions in 

 the floor of the anterior part of the medullary groove. In an 

 embryo 2.33 mm. long the medullary groove is practically 

 closed in front, but is stih open behind. The optic vesicles are 

 easily seen projecting outward, backward and downward from 



'The length in this case means from the tip of the nose. 



