138 JAMES O. FOLEY. 



forming univalent chromosomes. Each such univalent member 

 shortens and becomes transversely constricted. After dissolution 

 of the nuclear membrane, according to him, the chromosomes 

 unite at one end to form a long bar shaped (quadripartite) 

 bivalent which bends on itself and forms a ring. In the meta- 

 phase of the first meiotic division one member of each bivalent 

 goes to one daughter cell, the other to the other. If his obser- 

 vation is correct, this is an unusual type of reduction and is the 

 only case reported for the fishes. In Umbra the reduction 

 phenomena follow more closely the account given for Scyllium 

 by Moore ('95). Although transversely constricted chromo- 

 somes do appear in Umbra, as described by Agar for Lepidosiren, 

 they unquestionably occur in spermatogonial divisions in Umbra 

 and never during the time of meiosis. 



SUMMARY. 



1. The spermatogonia of Umbra limi are formed anew each 

 season from cells which migrate from some point outside the 

 lobule, possibly in some cases even from outside the testis. 



2. Evidence points to the presence of definite pro-chromo- 

 somes in the early spermatogonia. 



3. The somatic and spermatogonial number of chromosomes is 

 twenty-two. Chromosomes, at different times and in different 

 cells, may exhibit contractions of varying degrees. Extreme 

 contraction simulating a transverse fission is unusual. 



4. Two large L-shaped chromosomes, relatively constant in 

 size and shape, are found in all spermatogonial cells. They 

 may be sex-chromosomes. If so, the male of Umbra is of the 

 XX type. 



5. The multiplication divisions of the spermatogonia are in 

 general very rapid, \\iili the result that the final spermatogonia 

 are only of from one sixth to one third the volume of the original 

 ones. 



6. The primary spermatocytes of Umbra show roughly an 

 increase in nuclear size of 15 to 20 per cent, over the spermato- 

 gonia of the preceding multiplication division. 



7. The chromosomes emerge from synizesis in the form of rods 

 or blocks of chromatin of varying length and thickness. 



