no significant difference with respect to the ratio base
width: B ax® Total spermatozoan length (head, midpiece
and tail? %as the same in both fractions.

In the lower fraction there were significant positive
correlations between head length and total sperm length
T (r = 0.46, P<.0.0001), between head length and tail
length t (r = 0.33, P<0.01) and between head length and
total length of the flagellum (midpiece m + tail t)

(r = 0.33, P< 0.01). A negative correlation was found
between midpiece and tail lengths (r = -0.29,

0.02 P<0.01), pointing to a tendency of keeping the
ratio : (m + t) constant. In the upper fraction none
of these correlations was significant, indicating a
less homogeneous morphological composition of the upper
fraction.

 

Head length in the upper fraction of dog semen in
citrate was 6.8 + 0.04 pm, S.D. + 1.7 gnd in the lower
one 6.2 + 0.06 pm, S.D. + 0.38, P,«10™°. Head thickness
was 1.8 + 0.09 in the upper and 1.35 + 0.04 in the lower
fraction (P,< 0.002).

In human spermatozoa maximum head width was smaller
in the lower fractions (3.27 + 0.09 pm, S.D. + 0.58
vs. 3.59 + 0.10 pm, S.D. + 0.67, E<0.05), other head
dimensions being not significantly different. No dif-
ference in nuclear dimensions could be detected between
the upper and the lower fractions.

Cock spermatozoa (having a rather different head
shape, resembling a slightly bent banana) had longer
heads with a greater length:width ratio and a smaller
radius of curvature in the lower fractions. The magnitudes
of the differences were highly dependent on the osmotic
pressure of the medium (highest in hypotonic media)
causing different degrees of swelling or shrinkage of
the cytoplasm.

Active swimming velocities of bull and cock sperma-
tozoa, fractionated in egg-yolk media, were determined
photo-electrically. In both species the average active
swimming speed was significantly higher in the lower
frac?ions (difference 8 + 1% in the bull, 15 + 1% in the
cock).

By interferometry no differences could be detected
in thickness, refractive index or wet mass in the main
regions of the heads of bull sperms in these upper and
lower fractions. Apparently any shape and size difference
was restricted to the upper acrosomal part of the head,
suggesting that the larger heads in the upper fractions
had either a slightly larger acrosome or a more swollen

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