338 H. B. POLLARD. 



the central cavity is only indicated by the disposition of the 

 cells, and near the centre are seen several cells characteristic- 

 ally in mitotic division. In fig. 5, which is approximately in 

 a median vertical plane^ the corpus striatum and lower ex- 

 tremity of the brain are seen to be separated by a fairly well- 

 defined line extending from the indentation to the median 

 cavity between the optic stalks. The ectoderm in this section 

 is artificially deformed. It should continue over the yolk 

 exactly abreast of the indentation. The characteristic mitoses 

 are again seen near the central cavity. Where the latter is 

 fully formed — that is, in the immediate region of the optic 

 stalks — it is seen to be partially occupied by structures {Gp.) 

 which Henneguy (6) terms " globules parablastiques/^ but 

 which Goronowitsch regards as cell debris due to the manner 

 of formation of the central cavity. The same structures are 

 seen in section in fig. 7, b. 



The account here given confirms the observation of Gorono- 

 witsch made on the salmon^ that the neural axis ends approxi- 

 mately between the optic stalks. The indentation in Gobius 

 can but be regarded as a rudimentary neuropore. 



The brain at this first stage is approximately in the same 

 condition as the salmon brain of the sixteenth day. 



On the following day the brain of Gobius shows the same 

 characters, but with a slight general advance. The eyes are 

 becoming more rounded, and the optic stalk is being separated 

 from the eyes by a distal constriction. The lens is formed and 

 cut off from the ectoderm. Thus the development of the eyes 

 in Gobius proceeds more rapidly than in the salmon. No 

 choroidal fissure is as yet formed. The indentation which 

 marked the neuropore is less perceptible, though the exact 

 point where it occurred is still to be determined. The cavities 

 of the brain are well formed, and the vertical extent is less in 

 proportion to the breadth. The corpora striata, which in the 

 previous stage^ as shown in sections (figs. 6, 7), were only part 

 of the dorso-lateral wall of the neural tube, are now well- 

 marked thickenings, pushing the optic stalks downwards, and 

 giving rise to a slight cranial flexure. 



