i62 Journal of Comparative Neurology. 



lium. The ear-capsule, lense-capsule and sensory pits of the 

 head (in fishes) are to be included. The strong confirmation 

 which these views have recently received from the study of Am- 

 phioxus and Ammocetes is elsewhere referred to. 



It will be noticed that the surface from the angle of the 

 mouth to the nasal end of the head is nearly in one straight line. 



The next stage is from embryos taken June nth. Growth 

 during this period is very rapid and in order to secure consecu- 

 tive stages a large amount of material would be needed. The 

 lense has closed and separated from the skin. The gill clefts 

 have closed with the exception of a single pair. (The posterior 

 pairs were not made out as distinct openings in any of the speci- 

 mens examined.) The nasal sacs have been formed and extend 

 from immediately cephalo-ventrad of the eye toward the cephalo- 

 ventral aspect of the head. It can be readily seen that the 

 growth is from ventro caudad cephalo-dorsad ; i.e., that the 

 epithelium is driven up into the pits by proliferation in that di- 

 rection. In accordance with the suggestion just made, the 

 growth is from the pituitary region cdudad (morphologically) 

 and, as in Amphioxus the nasal and pituitary structures are asso- 

 ciated, so here at first the same relation prevails. It may also 

 be noted that the protrusion of the recessus opticus and the in- 

 fundibulum are causing the palatal area to be flexed. The 

 whole cerebral part of the head is being flexed dorsad, — as may 

 be seen by examining later stages. There is as yet no external 

 evidence of trunk segmentation but the medulla is strongly seg- 

 mented and produces a superficial node-like appearance behind 

 the ear. (Plate XVI, Fig. 3.) 



The third stage is represented by Eutaenia embryos taken 

 June 15th. The germinal disc covered three-fourths of the yolk 

 and the tail described three turns. (Plate XVI, Figs. 4, 5.) 

 The backward flexure of the front of the head is still more 

 marked and the nasal sacs are carried cephalo-dorsad. The my- 

 omers of the trunk and tail are prominent. 



In this stage the lense is beginning to fill out the capsule 

 and the retina has stongly differentiated from the pigment layer, 

 but the primary optic vesicle has not closed and the optic fibers 

 have not begun to appear. 



The pituitary is just forming and has not called out any re- 



