DEVELOPMENT OF THE HEAD IN GOBIUS CAPITO. 349 



shows the region of condensation of the mesoderm. In later 

 stages the tissue at the point of deepest ingrowth of the ecto- 

 derm of the mouth becomes less compact, so that then two 

 Anlagen may be distinguished. The upper grows forward, and, 

 with the diflferentiation of cartilage, gives rise to trabeculse, 

 intertrabeculse, and the tissue underlying the maxilla, as 

 described by Stohr (22). The lower gives rise to the lower 

 jaw. I hope to make the subsequent modifications which give 

 rise to the adult conditions the subject of a special study. The 

 fact that both upper and lower jaw structures arise as one 

 paired Anlage at the angle of the mouth appears to have interest 

 in view of the theories as to the presence and number of gill- 

 bars having relation to the mouth. 



Summary. 



1. The neural axis in Gobius terminates at a point near the 

 optic stalks, precisely as stated by Goronowitsch for the 

 salmon. An indentation and the disposition of the cells at 

 this spot indicate a rudimentary neuropore. In later embryos 

 a characteristic crucial lumen, which may be traced con- 

 tinuously from behind forwards, gives another indication of 

 the termination of the axis, and also shows that the corpora 

 striata belong to the upper part of the wall of the brain. 



2. Mouth and hypophysis arise as solid ingrowths of ecto- 

 derm. That the earliest and maximum ingrowths are inde- 

 pendent and paired is probably an embryonic feature due to 

 the mode of development of the brain and eyes. Nothing has 

 been observed to indicate that the mouth was ever anything 

 but a mouth. 



3. Skeletal structures of both upper and lower jaws arise 

 from one condensation of mesoderm round the ectodermic 

 ingrowth of the mouth. 



4. The jaw muscles do not arise from the " Seitenplatten " — 

 a point of considerable theoretical importance. 



Naples, 



March, 1893. 



