324 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



from a living post-larval specimen 4' 6 mm. long. The 

 prostomium bears six eyes, two of which, those first formed 

 in the larva, are larger than the others. Scattered over 

 the surface of the prostomium are groups of fine sense 

 hairs. Only those on the margin are shown in the figure. 

 x 100. 



Plate VIII. 



Figs. 60 — 65. The formation of spermatozoa. 



Fig. 60. One of the earliest stages found in the 

 coelomic fluid consisting of sixteen cells (spermatogonia), 

 x 500. 



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 500. 



Fig. 64. Two cells — spermatids — from 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 500. 



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 (1^). 

 x 100. 



