324 F. L. LANDACRE 



not yet in contact with the epidermis. Figs. 14, 15, 16, 44, 45, 46 

 were drawn from this stage. 



Stage V . Optic vesicle and optic stalk completely open. Lens 

 indicated by slight thickening of the epidermis. Auditory vesicle 

 with well defined cavity and the proliferation of cells from the 

 vesicle to form the ganglion beginning. Gasserian and geniculate 

 ganglia distinguishable from the loose lateral mass cells sur- 

 rounding them, although their boundaries cannot be definitely 

 determined. Hyoid gill pocket in contact with the epidermis. 

 First stage in the proliferation of cells from the auditory vesicle 

 to form the lateralis IX ganglion. Hyoid gill pocket in contact 

 with the epidermis. Figs. 10, 11, 13, 17, 18 and 63 were drawn 

 from this stage. 



Stage VI. Lens thickening well defined but changing gradually 

 at the borders into epidermis, i.e., not sufficiently thick to have its 

 borders well defined. First epibranchial placode appears. Hyoid 

 gill pocket still in contact with the epidermis. Figs. 19, 20, 21, 

 22, 23, 24 were drawn from this stage. 



Stage VII. Lens constricted sharply at its borders prepara- 

 tory to its detachment from the epidermis. Nuclei of cells in 

 lens not yet located in the periphery of the cells. First epibran- 

 chial placode is proliferating cells into the mesoderm to form the 

 first epibranchial ganglion but the ganglion is still in contact with 

 the epidermis. The jugular ganglion of the X can be located. 

 The lateralis X ganglion is in process of being proliferated from the 

 postauditory placode. Hyoid gill pocket still in contact with the 

 epidermis. Figs. 12, 25, 26, 27, 28, 29, 30, 40, 41, 42, 43, 47, 48, 

 49, 50, 51 were drawn from this series. 



Stages VIII — IX correspond closely to a forty-nine hour 

 embryo of Ameiurus melas being possibly slightly younger. There 

 seems to be no well defined distinctions between stages VIII-IX 

 or between these and A. melas forty-nine hours. The three figures 

 drawn from these two series could have been taken from A. melas. 

 Fig. 61 was drawn from Stage VIII and figs. 52, 62 from Stage IX. 



All sections were cut 7n thick and it will be convenient to ex- 

 press the spatial relations of structures in sections. 



