DAVENPORT: PROCESSES CONCERNED IN ONTOGENY. 187 
not inelude the lateral organs, — eye vesicles, gills, and arms, — which 
ariso in a similar fashion as folds. 
Based upon the form of the growing area, two classes of folds may be 
recognized : — 
(a). Pockets, from a circular area. 
(6). Linear folds, from an elongated area. 
[ASSI 
NECE 
Good examples of the formation of pocket folds are seen in many cases 
of gastrulation, and in the otocyst, shell gland, salivary gland, and sepia 
sac of Figure 18, 
Fig. 19. Two stages in the development of the epidermis and neural tube of the 
chick. Both magnified to the same extent. (From W. His, '94, Arch. f. Anatomie, 
Jahrg. 1894, pp. 74, 76 ) 
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