I2O JAMES O. FOLEV. 



give such lobules a superficial resemblance to the seminiferous 

 tubules of the higher vertebrates. Turner ('19) describes a 

 similar method of peripheral arrangement in the pickerel. There 

 is very little if any division of the primary spermatogonia 

 during this period in the testes. Each new spermatogonium is 

 formed by a process of growth from a migrating cell; once 

 established, it eventually becomes the center of a cyst within 

 the lobule. This process of cyst or pocket formation begins 

 at the periphery and gradually extends toward the center of 

 the lobule until the latter is filled with a solid cord of germ-cells. 

 Following the formation of this primary cord of cells, other 

 small migrating cells may be seen along the periphery of the 

 lobule or between the cyst walls during the period of migration 

 and growth which reaches its apex by the middle of July. Up 

 to this time few mitotic figures can be seen. From the middle 

 to the last of July there is a period of rapid multiplication of 

 the primary spermatogonia and in a number of the cysts the 

 cells have advanced as far as the first maturation division. By 

 the first week in August the cells in a number of cysts have 

 completed maturation and show various stages in the trans- 

 formation of the spermatids. During the remainder of August 

 and early September the various maturation stages are to be 

 found in abundance. By the middle of September a large 

 proportion of the testes are filled with spermatozoa. With the 

 completion of the transformation of the spermatids into sperma- 

 tozoa all evidence of cyst arrangement within the lobule dis- 

 appears. Just before and immediately after expulsion of the 

 spermatozoa, which occurs during the following season, there is 

 no evidence of cysts within the lobules. They are formed again 

 at the beginning of the next migration and multiplication period. 

 There is no antero-posterior seriation in the testis of Umbra; 

 each cyst completes its cycle as an independent unit. A cyst 

 in which late primary spermatocyte figures can be seen, however, 

 may also show earlier maturation divisions and some spermato- 

 gonia. Likewise secondary spermatocytes and transforming 

 spermatids may be found in the same cyst. This makes de- 

 tection of the different stages in the spermatogenetic cycle more 

 difficult. Another factor which complicates the study is the 



