The Reactions of the Vertebrate Embryo to Stimulation etc. 547 



Guthke's description of this nerve in Torpedo embryos of 

 11 mm. in length (Stadium 2) correspond to the conditions observed 

 at a very nmcli earlier period wlien the tissues have been stained 

 by a method capable of picldug out tlie neurofibrils. The differenee 

 between the stages represented by the embryos described in the 

 present paper and tliose mentioned by Guthke is even greater than 

 at first appears. The lengths of the embryos upon which my obser- 

 vations were condii cted were determined prior to fixation, while 

 Guthke's measurements were made after the material had been 

 fixed in sublimate and subsequently preserved in alcohol, so that 

 there must be a differenee of at least 5 mm. between my embryo 

 of 7 mm. in leng-th in which this nerve was clearly descernible and 

 the Stadium 2 of Guthke representing the conditions in embryos 

 of 12 mm. It has frequently been noted that embryos of this size 

 shrink at least 1 mm. during the process of fixation so that an em- 

 bryo of 11 mm. in length if measured in alcohol may be said to 

 be at least 12 mm. long when alive. 



The Ramus ophthalmicus superficialis of the Facial is not yet 

 ditferentiated. 



Several sectìons, each one 5 a in thickness, intervene between 

 the point at which the last fibril bundles forming the Trigeminus 

 root are seen entering the medulla, and that where those passing 

 into the Facial first make their appearance. In this interval within 

 the medulla a few bundles of fibril s in each section are seen in the 

 marginai- veil zone running in the direction of the anterior commissure; 

 while the cross sectìons of otliers connecting more remote centres 

 are also visible in this same location. When the Acustico-facial 

 ganglion comes into view large numbers of fibrils are already s.een 

 creeping in among the nuclei but are not yet visible in the epidermis 

 at the points where those two structures are in contact. Ali points 

 of the ganglion, those lying cranially as well as caudally, contain 

 a comparatively larger number of fibrils than does the Trigeminus 

 ganglion. 



After a break of ten or twelve sections, bundles of fibrils are 

 seen entering the Glossopharyngeus. The connections between the 

 ganglion and medulla are already numerous, a fact that is also 

 opposed to the observations of Guthke who refers to the compara- 

 tive uìeagreness of the connections existing between these two 

 masses. Not unfrequently thick bundles may be followed, extending 



