398 F. L. LANDACRE 



EXPLANATION OF FIGURES 



24 lies four sections back of fig. 23, the epidermis is reduced in thickness and 

 the placode is not so long dorso-ventrally. Just back of this the epidermis is of 

 normal thickness. 



25 to 30 (A. neb., Stage VII), illustrating the origin of the epibranchial por- 

 tion of the geniculate ganglon, are all from the same embryo which is slightly older 

 than the one from which figs. 19 to 24 were taken. Figs. 25 to 2S are consecutive. 

 Figs. 29 and 30 are consecutive, one section intervenes between figs. 28 and 29. 

 Fig. 25 lies near the posterior limit of the contact of the hyoid pocket with the 

 epidermis and fig. 26 at the extreme posterior limit. Active cell division is taking 

 place here. In fig. 27 the ganglionic mass is proliferated mesially over the hyoid 

 pocket which is no longer in contact with the epidermis. In fig. 28 the ganglionic 

 mass is still purely placodal in origin, but in fig. 29 the placodal ganglion is in 

 contact with a slightly delimited mass (L. M. G. VII) derived from the lateral 

 mass. In fig. 30 the lateral mass portion of the ganglion predominates. A few 

 sections posterior to this point the ganglion is entirely of lateral mass origin and 

 the epidermis is of normal thickness. 



31 to 39 (A. melas, 86 hours) illustrate the relations of the Gasserian ganglion 

 to the geniculate and the dorso-lateral and ventro-lateral lateralis ganglia of the 

 VII nerve. Figs. 37, 38 and 39 also show this relation to the auditory ganglion and 

 vesicle. Preceding the stage of 86 hours it is not possible to differentiate between 

 the two lateralis ganglia of the VII nerve and following this stage the ganglia 

 soon becomes condensed and it is difficult to unravel them. 



31 is taken throughthe trunk of the nerve (supero-lateral strand of Wright) of 

 the Gasserian ganglion. 



32 is taken just anterior to the point of origin of the nerve (infero-mesial strand 

 of Wright) of the geniculate ganglion. These two strands combine in a later stage 

 some distance from the ganglia and then split into the maxillary and mandibular 

 nerves. 



33 is taken through the root of the Gasserian ganglion. 



