12 The Unity of the Organism 



in processes of degeneration and disappearance; and that the 

 mitochondria, mi, look as though they had collected into two 

 well-defined spherical masses m.r., on the side of the cell oppo- 

 site the nucleus and near the small area of thinned-out striated 

 layer. As a matter of fact these two apparent mitochondrial 

 masses are the opposite sides of a ring seen in optical section. 



Transfoimiation of the general form of the spermatid now be- 

 gins by the indentation of the side opposite the nucleus, this 

 going on to produce first the quarter-moon shape shown at i.e., 

 figure 42c. By the still further growth and narrowing the edges 

 of the cup finally come together to produce the elongated cavity 

 shown in figure 42d, o.t. This is the beginning of the outer tube 

 which becomes long and relatively narrow as development con- 

 tinues, (figure 42e, ..). At an early period in the growth of 

 this tube the striated layer which naturally becomes shut into the 

 tube breaks up over most of the circumference of the tube into 

 what resembles a dense layer of long cilia. However, since the 

 processes are not motile and later dissolve and produce a gela- 

 tinous mass within the tube, their resemblance to cilia is only 

 superficial. This account of the fate of the striated layer applies, 

 as previously intimated, to most of the circumference of the outer 

 tube. But the small thin area of the layer opposite the nucleus, 

 shown in figures 42d and 42c, retains the cilia-like processes. 

 This persistent basal patch (b.p., figure 42d) is the starting 

 point for an important part of the future spermatozoon, the 

 "inner tube" so called by Doctor Casteel (i.t., figure 42e). 



While these profound changes are going on in the portion 

 of the spermatid opposite the nucleus, a stout, somewhat finger- 

 like process, (f.p., figure 42d) is formed on the nuclear side of 

 the spermatid, into the base of which the nucleus migrates. In 

 the meantime the vesicular bodies have entirely disappeared, and 

 the mitochondria, no longer disposed in the ring of earlier stages, 

 have assembled into an irregular, rather diffuse mass toward the 

 basal patch {mi., figure 42d). 



At the time when the outer tube has reached its maximum 

 length and is somewhat coiled, the inner tube, starting at the 

 basal patch previously described, begins to grow into the cavity 

 of the outer tube. This growth continues until the inner tube 

 is approximately as long as the outer tube. Figure 42e presents 

 an advanced but not completed stage of growth of the inner tube 

 i.t. In reality, according to Doctor Casteel's interpretation, the 

 inner tube grows at the expense of the outer tube, for when the 



