Il8 JAMES O. FOLEV. 



it number of different kinds of fish were collected (bass, 

 lurch, blue-gills, sunfish, stickleback, pickerel, carp, and mud- 

 minnows) and their testes preserved, sectioned, and examined. 

 After careful examination the mudminnow (Umbra Umi) was 

 selected as the most favorable specimen for study. Umbra 

 offers especially good material as the spermatogonial cells are 

 large, with the chromosomes in the form of L's and Vs. They 

 also show no great tendency to clump, hence individual chromo- 

 somes and chromosome pairs may be picked out with a fair 

 degree of certainty. The first maturation division is especially 

 clear, showing definite meiotic stages and clean separation of 

 the tetravalent chromosomes at the metaphase so that, in the 

 selection of this form, the writer believes that he has avoided 

 the main difficulties encountered by most investigators on fish 

 spermatogenesis, such as: (i) The small size of the germ-cells, 

 especially the primary and secondary spermatocytes; (2) the 

 small size of the chromosomes together with the fact that they 

 usually are in the form of threads, rods, or dots, rendering 

 counting extremely difficult and making it practically impossible 

 to follow them through the various stages in spermatogenesis; 

 and (3) the tendency of the chromosomes to clump badly. 



The purpose of the present paper is to try to clear up some 

 of the little known or little understood phases in the spermato- 

 genesis of the bony fishes. The writer wishes to express his 

 appreciation of the aid of Dr. A. S. Pearse in collecting specimens 

 and in reading the manuscript, of Dr. L. J. Cole for pointing 

 out the genetic application of the problem, and of Dr. M. F. 

 Guyer for suggestions in technique and helpful criticisms on the 

 entire work. 



MATERIALS AND METHODS. 



The fishes used in this investigation were collected in the 

 vicinity of Madison, from Lake Mendota and from various small 

 streams which empty into Lake Mendota and Lake Wingra. 

 Collections of Umbra limi were made once a week and testicular 

 material was fixed every day, or every other day during the 

 time the cells in the testes were undergoing proliferation. The 

 testes are two elongated white bodies situated in the posterior 

 part of the body-cavity just ventral to the swim-bladder. They 



