IQO CARL L. HUBBS. 



found to contain only one young, partially protruding from the 

 oviduct, and of the same size as numerous others recently born, 

 found swimming about in the same body of water (Hubbs, 1917). 

 In Amphigonopterus aurora also it is probable that, copulation 

 having taken place during the breeding season in the summer, 

 the spermatozoa are retained in the females until winter (or pos- 

 sibly late autumn or early spring), when fertilization occurs and 

 whence intramaternal development proceeds for several months ; 

 and that, therefore, one year elapses between the time of copula- 

 tion and the birth of the young. Six lines of evidence lead to, or 

 are at least not inconsistent with, these conclusions. 



1. This condition apparently holds in C y mat og aster aggregatus, 

 a distantly related species in which the breeding season is ap- 

 proximately synchronous with that of the present species, the 

 structures correlated with viviparity similar, and in which the 

 adults, and the young at birth, are of similar size to those of 

 Amphigonopterus aurora. 



2. Females taken in the autumn contained no young, and males 

 secured on October 26, November 25 and April I had small and 

 obviously non-functional testes, whereas all of the males taken 

 with the breeding females in the summer had mature testes. This 

 is true also of Micrometrus minimus, and perhaps of all embio- 

 tocids. 



3. The smallest embryos, only 12 mm. long to the caudal fin, 

 taken from any of the females secured in June, would presum- 

 ably have attained their full embryonic size (about 30 to 35 mm.) 

 late in the summer, toward the end of the breeding season. This 

 fact suggests a moderately long period of gestation; the largest 

 females, which at this time were bearing young, presumably had 

 contained embryos for several months. A similar situation holds 

 also in the case of Micrometrus minimus. 



4. The largest females, which produce young early in the sea- 

 son, were found to be in a spent condition, not containing a new 

 lot of embryos, during the months of July and August. Although 

 the data are less complete, this condition appears to hold also in 

 the case of Micrometrus. 



5. The fact that the smaller yearling females bear fewer young 



