ZOOLOGY. 411 



to test this hypothesis is difficult to obtain. Our cutleri crosses are 

 verj' good in this respect, since one race is fully twice as large as the 

 other and the hybrids are fully fertile, while not extremely variable. 

 The Fi generation is about as large as the larger race, but F2 is inter- 

 mediate between the parent races. There is no significant difference 

 in variability between Fi and F2. This result shows that the large size 

 of Fi is not due to MendeUan dominance, but to physiological vigor; it 

 is not inherited at all, for it disappears in F2. 



We shall have to seek further for the law of size inheritance, unless 

 we are content with the statement that size blends in heredity. Of 

 course it is conceded that MendeUan factors often affect size, as in 

 brachydactylism in man and in Dexter Kerry cattle, but that all factors 

 or that even the principal factors affecting size are MendeUan seems 

 extremely doubtful. Size in mammals seems to depend on general 

 properties of the protoplasm rather than on special (localized) ones. 

 MendeUan inheritance, on the other hand, involves locaUzed determiners 

 within the germ-cell, without which independent inheritance of 

 characters is scarcely conceivable. In this connection it is interesting 

 to note that we have discovered in rats two MendeUan characters which 

 seem to have determiners located adjacent to each other in the germ-cell, 

 so that ' ' coupling' ' or " Unkage' ' results. Such phenomena, well known 

 for plants and insects, have not previously been recorded for a mammal. 



The only extensive pubUcation made since my last report is No. 205, 

 by Dr. Detlefsen, which deals with the results obtained from Cavia 

 rufescens crosses. Nine shorter papers deaUng with particular phases 

 of our experiments are included in the bibUography. (See Castle, Fish, 

 Wright.) Particular attention is called to the paper by Castle and Had- 

 ley, which contains a brief report upon an investigation extending over 

 several years carried out at the Rhode Island Agricultural Experiment 

 Station in collaboration with Dr. Hadley. 



My faithful assistants during the past three years, Messrs. Wright 

 and Fish, are leaving on September 1 for positions of larger opportunity, 

 the former to conduct investigations in genetics in the Bureau of 

 Animal Industry, U. S. Department of Agriculture, the latter to be 

 professor of zoology in Denison University. It is hoped that their 

 valued service in these investigations may have fitted them for added 

 usefulness in their new fields of labor. An extensive pubUcation by 

 Wright and myself on inheritance in guinea-pigs is in preparation. 



Naples, Zoological Station, Naples, Italy. Maintenance of two tables for 

 American biologists. (For previous reports see Year Books Nos. 2-13.) 



The Director of the Station reports that on account of the Eiu-opean 

 War no Americans have visited Naples to make use of the tables sup- 

 ported by the Institution. 



