PLATE 1 
EXPLANATION OF FIGURES 
1 Ammocoetes, 1.5 em. Transverse section through the posterior part of 
the forebrain. 
2 Ammocoetes, 3 cm. Transverse section through the opening of the caudal 
ventricular diverticulum. 
3, A,B Transverse sections, A, through the ‘primordium hippocampi’ of 
Petromyzon, B, through the ‘eminentia thalami’ of Triton. 
4 Ammocoetes, 3 cm. Transverse section through the opening of the olfac- 
tory ventricle. 
5 Acanthias, 3.3 em. Transverse section through the foramen monroi. 
6 Acanthias,3.3cem. Transverse section through the middle of the forebrain. 
Same series as figure 5. 
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