374 THOMAS II. MONTGOMERY. 



the same length and lie close together. In their later stages 

 (Figs. 43, 46, 47) these secondary rodlets undergo some increase 

 in thickening, and in all cases these rodlets persist within the 

 Sertoli cell until the end of its cycle; they also probably degenerate 

 there, for no signs of them were found within the germ cells or 

 free in the fluid of the seminiferous tubule. 



But in one fifth of the cases, 19 out of 100 cells examined, 

 the original rod continues visible for a shorter or longer period 

 after the secondary rodlets have been produced, as shown in 

 Figs. 35-30, 42, 45; and in Fig. 41 is drawn an unusual case of 

 late persistence of the rod and primary rodlet together. The 

 rod may persist for a while as a single dense body (Fig. 38). 

 Fig. 30 shows a case of such a single rod that has segregated into 

 chromatic and achromatic parts, a rare condition. But as a rule 

 it divides longitudinally as exhibited in Figs. 35-37, 41, 42, 45; 

 this division begins and is most prominent near the middle region 

 of the rod, when its ends may be still undivided, but cases were 

 found where the rod had completely divided into two secondary 

 rods (Figs. 35, 40, Fig. 40 being a rod from a cell of about the 

 stage of the cell shown in Fig. 30). In the instances where the 

 rod persists after the secondary rodlets have been produced, it 

 never stains quite as deeply as the latter, and gradually becomes 

 less and less chromatic until it can no longer be seen; no rod 

 was observed in any cell after the karyosphere of the nucleus had 

 disintegrated. 



There is accordingly considerable individual variation in the 

 behavior of the rod after it has abstricted the primary rodlet; 

 in four fifths of the cells it then promptly disappears, in one fifth 

 it persists for a variable period, but never until the end of the 

 cycle of the Sertoli cell, and then undergoes a second longitudinal 

 division which is this time an equal division. The rod when it 

 persists generally remains in the basal portion of the cell body. 

 The secondary rodlets arc at first usually in contact with the 

 surface of the nucleus, either basal or distal, while they are later 

 found near the distal pole of the nucleus and usually sep.ir.iied 

 from it. Whether the disappearing rod contributes substance 

 to the formation of the fibers in the cytoplasm (Fig. 43) could 

 not be determined. It is also difficult to decide whether the 



