438 Sidney I. Kronhauser 



Tliat oöcytcs and spermatocytes can be produced from the same 

 uiireduced cells (oögonia) of a hermaphrodite has been shown to be true 

 for Rhaiditis, the distinction being first evident by the difference shown 

 in the behavior of the hetero-chromosomes (Boveri. '11 ; Schleif, '11). 

 In the spermatocyte divisions of RhaMüis an eUmination of one of the 

 hetero-chromosomes follows, so that two classes of spermatozoa are 

 formed. In such a hermaphroditic gonad as that of Figure 4, it is likely 

 that there is also a regulation which takes place early in the growth period, 

 if not before this, which decides which cells shall be oöcytes and which 

 spermatocytcs. Considering how sniall a percentage of the immense 

 nuniber of spermatozoa produced ever come to active fertilization, there 

 is but little chance of finding an individual which had been produced 

 by the union of a spermatozoa of the + class (Fig. I) with an egg. It is 

 therefore not remarkable that only one hermaphrodite w^as found among 

 the eight thousand (6000 o : -ÖOO 2) specimens which were sectioned. 



X. Summary. 



1. In the testes of Hersüia the regulär sequence from the sperma- 

 togonia to the spermatozoa make a perfect seriation of the stages possible. 

 The ovaries, up to the "confused stage" in the oöcytes, show the same 

 seriation. 



2. There is a medium unpaired " Keimpolster" in both sexes. It 

 is separated from the gonad proper Ijy a membrane. The cells of the 

 "Keimpolster" are of an entirely different character than the spermato- 

 gonia or oögonia, and neither in immature individuals nor in adults is 

 there any evidence that the "Keimpolster" givcs rise to the germ cells. 

 It is more probably a nutritive organ. 



3. In the spermatogonia and oögonia there are twenty-four chromo- 

 somes. Twenty-two show a "Querkerbe"; two are without this struc- 

 ture. The "Querkerbe" is not across the middle in at least two pairs 

 of chromosomes. The prophase chromosomes do not arise from the 

 segmentation of a spireme, nor do the telophase chromosomes unite 

 to form a spireme. In the quiescent spermatogonium there are usually 

 two nucleoli, and on the nuclear membrane in the cytoplasm are 

 disks which stain similar to the nucleoli. These have been named the 

 "cyto-plasmosomes". 



4. The leptotene threads arise separately from the network 

 following the ultimate spermatogonial division. There is at no time 

 a spireme formed which segments into these threads. The leptotene 



