86 
J. E. BLOOMFIELD. 
velopment consists in a growth in length, both of the rod-like 
and lash-like portion. 
The pear-like shape of the spermatoblast gives place to an 
elongated oval with a conspicuous knob-like head, from which 
proceeds the lash-like filament. The elongated oval grows into a 
short rod with a prominent cap. The short rod then grows into 
a comparatively long one, till the length of a mature spermato- 
zoon is attained, though the distinction of nucleus “cap” and lash 
may be traced as long as the sperm rod is attached to the central 
blastophor (figs. 43 — 48). In the mature spermatozoa the 
nuclear portion is only distinguishable from the rest by its rather 
greater thickness. When the sperm cells reach the stage of 
mature spermatozoa they fall off from the blastophor and find 
their w^ay into the ciliated vasa deferentia. The further fate of 
the blastophor it is hard to decide. It has no nucleus, but 
sometimes a vacuole is visible (fig. 49). Often it is pigmented, 
and it is probable that it atrophies, having served its purpose of 
a support to the spermatoblasts. 
The blastophor or central mass of the earth-worm's sperm- 
polyplast possesses a very high interest, and will be found to be 
represented, I believe, in the development of the spermatozoa of 
most members of the animal kingdom. I have seen it in 
Hirudo, in Helix (PI. VI, fig. 73), and in Rana (fig. 74) and Sala- 
mandra. In the two latter it is nuclecdedy a difference from the 
earth-worm, which I endeavour to explain in the next paragraph. 
General conclusions. — I have found no consistent account of 
the development of the spermatozoa of the earthworm, though 
isolated phases of the ^ sperm-polyplasts ’ have been from 
time to time noticed and figured in text-books of histology. 
Prom observations, which I am still pursuing, upon other animals, 
I am inclined to think that what we find in the earthworm is 
fairly typical of a large number of other organisms, including 
Mollusca and Yertebrata. The general notions on the 
subject appear to have made little or no advance since 
Kolliker's paper, published in 1856 (^Zeitsch. fur wiss. 
Zool.,' Bd. vii), which is, as might be expected from its date, 
w'anting in accuracy. Kdlliker gives very unsatisfactory 
drawings of the development of the spermatozoa of the bul- 
lock, the pigeon, the frog, and the carp. His ^ mother-cell ' 
corresponds to my ^ polyplast,' but he complicates the whole 
history by erroneous notions as to endogenous cell formation 
and the conversion of nuclei into spirally rolled spermatozoa. 
The result of my observations is that, to begin with, the nucleus 
of the prmUive cell or spermatosporc in the young testis is of 
unusually large size, and that the secondary nuclei to which it 
givL's rise stand out around the central mass or blastophor of the 
