218 PROCEEDINGS OF THE AMERICAN ACADEMY. 



phisni to heredity, and in the brook trout the effects of altered action 

 of gravity during development, together with the results obtained from 

 the study of monstrous specimens and from the development of the 

 optic nerves. The work on the inheritance of the optic chiasma was 

 begun by Dr. W. E. Castle and Mr. F. E. Pomeroy, and was carried 

 on and completed by the writer under the direction of Dr. Castle, 

 to whom the writer wishes to acknowledge his great indebtedness 

 for the material placed at his disposal and for aid and criticism dur- 

 ing the progress of his studies. He is also grateful to Mr. Pomeroy 

 for the use of results obtained by him at the beginning of this investi- 

 gation. Thanks are due also to the Massachusetts Commissioners of 

 Fisheries and Game, and in particular to Mr. Arthur Merrill, super- 

 intendent of the fish-hatchery at Wilkinsonville, Massachusetts, for 

 supplying and rearing the brook trout material ; also to the officers ot 

 the Bureau of Fisheries of the United States Department of Commerce 

 and Labor who supplied and reared at Wood's Hole, Massachusetts, 

 the young codfish used. 



Object of the Investigation and the Method employed. 



The writer has already hinted at the object for which this investiga- 

 tion was undertaken. The main object was to test the relation of 

 heredity to the dimorphism of the chiasma, and especially to determine 

 the applicability of Mendel's Law, should heredity prove to be a factor 

 in this dimorphic condition. In order to determine whether or not 

 heredity is a factor, matings of selected individuals were made, and 

 the effects determined by dissecting the young. For this purpose two 

 species offish were used, the common brook trout {Sal celt mis font inalis 

 Mitchill) and the codfish (Gadus morrhua L.). Since the spawning 

 season of these two is mainly during the months of November and 

 December, they were especially convenient forms with which to work. 

 In making these matings, the eggs of a female were commonly divided 

 into two or three lots, and each lot fertilized artificially with the milt 

 of a different male. The parents were then dissected to determine the 

 position of the nerves in the chiasmata ; the different lots of eggs were 

 carefully marked, and the necessary data recorded for future use. 

 This part of the work was done by Dr. Castle ; the study of the first 

 generation of brook trout and of the first lot of young codfish was 

 begun by Mr. Pomeroy and completed by the writer, who also carried 

 out the remaining studies described in this paper and prepared this 

 report for publication. 



In preserving the two species of fish for study, different methods 

 of fixation were found necessary. The young trout were of suffi- 



