EDWARD DRANE CRABB. 



EXPLANATION OF PLATES. 



The figures of all the plates have the same reduction and all, except 

 Figs. 8, 9, 10, 17, 18, 44, 45 and 46, were outlined with the camera using 

 loX ocular and 1.9 objective (scale 0.03 mm., Pis. 4, 5) or i8x ocular and 

 1.9 objective (scale 0.02 mm., PI. 5). 



PLATE i. 



Free ova from the acini of the ovotestis near the beginning of the free 

 hermaphrodite duct (region H, Fig i, Crabb, '276), except Fig. 6, scale 

 0.03 mm. 



FIG. i. A recently ovulated egg completely enveloped by the hyaline 

 membrane (HM) ; germinal vesicle intact. Burkhardt and cane sugar, 

 6 fJ-, iron-hsematoxylin. 



FIGS. 2, 3, 4, 5. Fragments of two centrifuged ova which have recently 

 lost the hyaline membrane. The yolk granules have been dispersed and in 

 addition the peripheral region is badly fragmented, thus making it an easy 

 matter to trace the spermatozoa in the cytoplasm. Fig. 3 represents a 

 section of a large peripheral fragment and shows numerous spermatozoa. 

 The living snail was centrifuged 15 minutes and immediately killed in 

 Burkhardt's solution and NaCl at 48 C, 6 M, iron-haematoxylin. 



FIG. 6. An inseminated egg from the hermaphrodite duct (L to O, Fig. i, 

 Crabb, 27^). Reconstructed from two non-consecutive sections. The ger- 

 minal vesicle and round sperm heads without tails are from one section, 

 while those having tails are from a peripheral section. Perenyi, 6 p, iron- 

 haematoxylin. 



