100 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
cyst cells also increase in size. The nuclei in them become large and 
distinct, fairly rich in chromatin. This forms a loose network. 
As one of these lateral cyst cells grows, it gradually surrounds the 
bundle of sperm cells, and finally coalesces on the opposite side, thus 
forming a ring or tube (pi. 14, fig. 52, c. c.). Hence beginning at the 
head nurse-cell (pi. 14, fig. 43), there is a single row of these tubular 
cells gradually diminishing in thickness, but broadening out antero- 
posteriorly toward the tail end of the cyst. In one or two instances 
one of these cells has been seen at the extreme end of the cyst, but 
these are rare exceptions. 
History of the Head of the Spermatozoon. 
The spermatozoon has now acquired its definite length, and the 
tail probably is completed. The head of the spermatozoon is now 
so intimately related to the head nurse-cell, being imbedded in its 
cytoplasm, that these have to be considered together. While the head 
nurse-cell is growing rapidly, the original nucleus of the spermatozoon 
(pi. 14, fig. 50) elongates enormously (pi. 14, fig. 44). The remark¬ 
able regularity in the length of these nuclei, their perfectly parallel 
arrangement, their homogeneous appearance, and their uniform stain¬ 
ing in nuclear stains are very striking. I have found it difficult to 
make my drawings as diagrammatic as these sperm heads, taken 
together, appear under the microscope. 
The aerosome .— At this stage (pi. 14, fig. 44), we find again evidence 
of the position of the eentrosome. The anterior end of the cell has 
become greatly attenuated and elongated. This has penetrated the 
spongy cytoplasm of the head nurse-cell till it nearly reaches the 
nucleus, the nurse cell having at the same time developed greatly. 
Near the middle of this anterior portion of the sperm cell, the centro- 
some occupies a little vacuole in a slight enlargement of the cytoplasm. 
All these taken together form a row running parallel to the anterior 
ends of the greatly elongated nuclei (pi. 14, figs. 43, 44, 48, 54). They, 
too, are imbedded in the head nurse-cell. The elongated nuclei take 
the green of the Biondi-Erlich triple stain; the centrosomes are emi¬ 
nently cytoplasmic, being made distinct by orange G and acid fuch- 
sin and saffranin. 
Transverse section through the elongated nuclei is represented in 
