REPRODUCTION — SPERMATOZOON. 
375 
are usually first developed aud are arranged with their heads to the 
walls of the gonad in intimate connection with the nutritive cells, and 
are shed from the germinal epithelium in the form of mother cells or 
Fig. 692. Fig. 693. Fig. 694. Fig. 695. Fig. 696. 
Development of the Spermatozoa of Cyclostoma elega7ts (Mull.), highly magnified (after Garnault). 
Figs. 692, 693.— Groups of Spermatogonies. Fig 69A. — Group of Spermatocytes. 
Fig. 695. — Cluster of immature Sper'natozoa. Fig. 696. — Maturing and mature Spermatozoa. 
Fig. 697. — Dimorphic sperma- 
tozoa of Vivipa7‘a vivipara (L. ), 
greatly magnified (after Recluz). 
spermatocytes, which mature and separate into their constituent 
spermatozoa whilst free within the lumen of the lobule, the ova 
retaining their position upon the epithelial walls until mature. 
In certain dioecious species two forms of .spermatozoa may be found 
— an elongate one with a caudal filament 
and spirally twisted head, the other long, 
cylindrical, and slender, without any 
cephalic enlargement, but with a terminal 
tuft of extremely fine filaments; these are 
affirmed to be formed by an agglomeration 
of miniature spermatozoa and were at one 
time regarded as parasitic organisms, 
Ehrenberg applying the name of Phacelura paludinw to the form 
peculiar to the Paludinidw. 
The spermatozoon has a vermicular or axial rotatory motion, and 
when in contact with the egg has been noted in some forms of life to 
move around the ovum in regular circles 
of varying orbit, so that it eventually 
meets the micropyle or minute aperture 
leading to the interior of the egg, fusing 
with the protoplasm projecting therefrom 
and losing its enveloping membrane, 
which fuses with the egg membrane 
and closes the micropyle against other 
spermatozoa. If polyspermy results owing 
to cold or weakness of the ovum it may give rise to abnormal offspring. 
Fig. 698. — Fertilizing receptacle of 
Succinea puiris (L.), X 20 (after 
Ihering), showing its connection with 
the seminal %esicles, etc. 
7>.s. seminal vesicles ; h.d. herma- 
phrodite duct ; ov. oviduct ; v.d, 
vas deferens. 
