284 F. B. SUMNER. 



of deferred fertilization, a phenomenon which has been little 

 recognized among mammals. It is stated by Marshall (1910, 

 p. 136), on the authority of various investigators, that "in certain 

 bats copulation is performed during the autumn, whereas ovula- 

 tion is postponed until the following spring, the animals in the 

 meantime hibernating, while the spermatozoa are stored up in 

 the uterus." There is no inherent improbability of the occur- 

 rence of parallel phenomena in rodents. The presence in the 

 uterus of active spermatozoa long after copulation ought, 

 however, to be directly determined for these animals. 



A few additional comments seem worth while before closing 

 these notes. It must be pointed out that, in Peromyscus, at 

 least, the phenomena discussed cannot be of very rare occurrence. 

 The seven cases in the first table which relate to deer-mice have 

 been observed in the course of rearing about 250 broods of young. 

 Thus nearly 3 per cent, of the litters born were followed by these 

 deferred or supernumerary broods. Whether or not the small 

 size of these first litters (i to 3 young) is a matter of signifi- 

 cance I cannot conjecture. 



Furthermore, it should be stated that most of these super- 

 numerary litters comprised normal, healthy animals, more than 

 80 per cent, of which survived nearly or quite to maturity. In 

 the great majority, at least, of the cases recorded for man, one, 

 if not both, of the fetuses has been dead or imperfectly developed 

 when born. 



Again, it is worthy of remark that in four cases out of eight 

 the parents of these supernumerary broods were both very young 

 mice, which had not yet been separated according to sex, while 

 in two more cases the fathers (though not the mothers) were very 

 young animals. Since the proportion of all my broods born of 

 parents of such an early age is very small, it seems likely that 

 this fact is of some significance. 



Finally, the possibility suggests itself that some of the alleged 

 instances of "telegony" which are recorded from time to time, 

 may result from the actual retention of spermatozoa received 

 from an earlier mate. A later copulation with a different partner 

 might happen to coincide with a conception in which the earlier 

 insemination was really the effective one. 



