204 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
great many cells or spermatozoa, the dark portions indicating, however, 
only the heads of the zoosperms, the tails being many times longer, but 
very pale ; it will bo noticed that the shape of the bundles changes from 
above downwards, being broad with rounded ends in the upper part, 
and becoming narrower and sharply pointed lower down. In the third 
segment [III] the interior of the tube is entirely filled up with the long 
tails of the spermatozoa, the tails belonging to each set of heads being 
themselves gathered into a sinuous bundle, which are perhaps fifteen or 
twenty times as long as the bundles of the heads. Finally, the fourth 
segment is filled with globules of various sizes, highly colored by the 
haeinatoxiline, very slightly refringent, and closely crowded together, 
leaving room only for small interspaces and a few bundles of spermatozoa 
tails which extend down among them. 
Before entering into the description of various details, which can be 
studied on the isolated tube, I will describe a transverse section through 
the upper part of the first segment, such a section as is represented in 
Fig. 24. The whole tube is formed by an external membrane, Tu., and 
its interior is divided up by septae, cys., into several distinct cavities, the 
spermatocysts, each of which contains a number of cellular elements, the 
spermatoblasts, all in about the same stage of development. In the 
walls of the spermatocysts there are a number of peculiar nuclei, so 
flattened that in a transverse section they appear as hardly more than 
a narrow dark line, as is indicated in the figure. The cells of the sperm- 
atoblasts are large and distinct, and are destined to be transformed each 
one into one or more spermatozoa. Near the top of the tube the sperm- 
atoblasts are round cells, the protoplasm of which is highly tinged with 
hoeniatoxiline, and which are provided with a bulky central nucleus each, 
as is shown in Fig. 2G. The nuclei are approximately spherical and very 
coarsely granular, the granulations being dyed almost black by hsema- 
toxiline. Judging from the analogy with other animals, the parts just 
described must be interpreted as follows : The whole of each spermato- 
cyst arises from a single cell, in which the original single nucleus gives 
rise by division to the secondary nuclei, each of which becomes a sperm- 
atoblast, the original cell enlarging until it becomes a cyst ; the mother 
nucleus also divides into nuclei like itself, which become transformed 
into the peculiar nuclei before mentioned, in the wall of the cyst. This 
is of course all hypothetical, not based upon direct observation, for in 
all the seminiferous tubes I have had an opportunity of examining the 
cysts and spermatoblasts were all fully formed. The most complete and 
satisfactory account which I am acquainted with of the development of 
the spermatozoon is that given of the frog by La Vallette. 283 I would 
also refer those who wish to understand the great theoretical importance 
of these facts to the brief summary of the observations previously made, 
which I have published elsewhere. 284 
283 La Vallette: Archiv fur Mikros. Anat., Bd. xh, s. 797, Taf. xxiv, xxxv (1876). 
^Minot: Theory of Impregnation. Proo. Boston S. N. H"., 1877, vol. xix, p. 165. 
