DAVENPORT: PEOC ESSES COXCEKNED IN ONTOGENY. 



185 



club-shaped pouclies as the "club-shaped glaud " of the Amphioxus 

 larva (K. & H., Fig. 875). 



c. Through unequal growth of the different meridians of a splieroidal 

 or cylindrical wall we have produced from the spheroid an apparent 

 flattening on one face, such as occurs, for example, in various cases of 

 "epibolic gastrulation." In Figure 16 this process is illustrated in the 

 spheroidal egg of a Heteropod. (Cf. K. & H., Figs. 66, 541, 738.) 



Fig. 15. 



Fig. 16. 



By an excess of growth along the meridians of one side of a cylinder 

 we have produced such apparent rotations of the internal organs as 

 occur in Crinoids and Eudoprocta. (K. &, H., Figs. 218, 732.) 



/8. Let us now consider the unequal areal growth of a part of a 

 bounding layer taken so small that it may be considered as nearly a 

 plane or a warped surface. We shall find that the processes taking 

 place in such a part are among the commonest and most important 

 of all occurring in ontogeny. 



This unequal growth may result, either (2) in parts formerly lying in 

 one plane moving into different planes; or (3) in parts formerly lying 

 in one line moving out of that line. 



2. It has long been recognized that, when in a laj'er excessive growth 

 takes place over a restricted area, the result is that the excessively 

 enlarged area can no longer occupy its former territoi-y. Since its 

 periphery remains relatively constant while the included layer increases 



Ficr. 15. Section tlironph the planiila of ^T^^qnorea, to show tlie greater expanse 

 at one pole tlian at the other. See K. & H , Fig. 14. 



Fig. IG. Sections through young embryos of Firoloides, showing how the condi- 

 tion in stage B has been derived from that of stage A by greater growth along the 

 meridians on the left than on the right. See K. & H., Fig. 584. 



