236 N. M. STEVENS, 
conclusively that the sperm-head is formed directly from the nine 
chromosomes from the last spermatocyte division. 
In the majority of cases all the cells of a group are in nearly 
the same stage, but there is sufficient overlapping to show the re- 
lation of the stages; for example, all the stages from Fig. 30 to Fig. 37 
may be found in different parts of one large group. 
As to the value of the two spermatocyte or maturation divisions, 
it is difficult to come to any satisfactory conclusion. The first divi- 
sion appears to be a reducing division in the WEISMANN sense, a 
separation of bivalent chromosomes into their original constituents, 
but who can tell what internal changes and shifting of elements may 
have occurred during the growth and subsequent shortning of the 
chromosomes? The spherical form of the daughter chromosomes of 
the first division makes it impossible to say whether the second 
division is transverse, longitudinal, or neither the one nor the other. 
The principal points where my results differ from those of LEE 
(1887) are: 1) in regard to the number of chromosomes, which he 
gives as eight; 2) in the character of the second maturation division, 
where he figures eight chromosomes in the equatorial plate and four 
at each pole; 3) in the method of formation of the sperm-head. 
The most striking elements among the sperm cells of Sagitta are 
the cells of the growth period preceding the two maturation divisions, 
where the chromosomes appear as nine large, very regular crenate 
loops (Figs. 24 and 25). The large number of such cells in nearly 
every section indicates that this period is one of considerable duration. 
A somewhat similar growth stage is figured by LEE (1897) in the 
spermatogenesis of Helix pomatia. 
IsHikAWA (1891) describes maturation divisions in the spermato- 
genesis of Diaptomus which bear some resemblance to those of 
Sagitta. The chromosomes have the same form and divide in the 
same manner in the first division, but the somatic number is present, 
and in the second division, though they assume the same dumb-bell 
form, one half of the number go to each pole. 
At some future time I hope to be able to study the embryological 
development of the ovary of Sagitta, to examine the ova when they 
are on the point of leaving the ovary, and to do some further work 
on the spermatogenesis by other methods. 
Zoologisches Institut Würzburg, 
Germany, July 31, 1902. 
