Evidence from Metazoan Germ-Cells 13 



two are of nearly equal length the entire spermatozoon is only 

 about half as long as it was before the inner tube developed. 

 All of the mitochondria of the cell are drawn into tlie inner tube 

 as it grows, and finally form a deeply staining mass at the distal 

 end of the tube {mi., figures 42e and ^ag). 



During these transformatory operations tlic nucleus, greatly 

 reduced in size proportionally to the sjiermatozoon as a whole, 

 has left its former place at the base of the finger-like j)r()eess, 

 and been making its way along the wall of the outer tube, bur- 

 rowing through the gelatinous layer on the outer })art of this 

 tube {n, figure 4<2e). This migration continues until, when the 

 distal end of the inner tube reaches nearly the end of the outer 

 tube, the nucleus lies in the wall of the outer tube opposite the 

 end of the inner tube {n, figure Igf.) 



The final act of transformation takes place after the sperm 

 has left the male tick and lies in a spermatophore sac within 

 the genital ducts of the female. This act begins with the per- 

 foration of the end {a. figure 42f) of the outer tube by the 

 inner tube. Through the opening thus made the whole inner tube 

 finally passes, really by a slipping back of the outer tube, so 

 that, the eversion of this latter being completed, the two tubes 

 constitute one continuous tube. By this act of turning inside 

 out, the finger-like process in which the nucleus formerly lay 

 (figure 42d, f.p.) is brought into close proximity again with the 

 nucleus. 



Some of the details of the final steps in the transformation 

 Doctor Casteel has not yet been able to make out ; but these 

 are of little consequence for our discussion. Nor has the 

 act of fertilization been observed. Going on the usual cri- 

 teria, the end of the sperm containing the nucleus would be 

 regarded as the head. But surprisingly enough, in moving, 

 the opposite end, the end containing the mitochondria, goes 

 foremost. 



This sperm and its development are so unicpie as con- 

 trasted with those occurring in most animal groups, that 

 one might be almost inclined to question whether there may 

 not be something wrong here — whether the case may not be 

 one of diseased growth, or the result of manipulative mal- 



