244 
from a living post-larval specimen 46mm. long. The 
prostomium bears six eyes, two of which, those first formed 
in the larva, are larger than the others. Seattered over 
the surface of the prostomium are groups of fine sense 
hairs. Only those on the margin are shown in the figure. 
x) 100. 
Puate VITI. 
Figs. 60—65. The formation of spermatozoa. 
Fig. 60. One of the earliest stages found in the 
celomic fluid consisting of sixteen cells (spermatogonia). 
x 900. 
Fig. 61. Optical section of a similar stage showing 
eight of the spermatogonia arranged round a vesicular 
residual mass of protoplasm—the blastophore. x 500. 
Figs. 62, 63. Later stages produced by continued 
division of the spermatogonia. x 4500. 
Fig. 64. Two cells—spermatids—trom a stage much 
later than the preceding. At one end (the left) of each is 
a small mass of protoplasm which later forms the apical 
body of the sperm, following this is the nucleus and a 
clear substance from which the middle piece of the sperm 
is derived, while on the right the protoplasm is being 
drawn out to form the tail. x 2000. 
Fig. 65. A discoidal mass of almost ripe spermatozoa. 
x 900. 
Fig. 66. A ripe spermatozoon. The head is divisible 
into an apical body, the nucleus and the middle piece, 
which is notched behind to receive the tail. x 3000. 
Fig. 67. A ripe egg from the body cavity. The flat 
face is shown. ‘The nucleus is large and vesicular, the 
yolk granules in the protoplasm are rather more numerous 
around the nucleus, the vitelline membrane is thin (1p) 
x LOO. 
