DAVENPOKT: PROCESSES CONCERNED IN ONTOGENY. 



195 



Sacculina, where the thorax and abdomen are thrown ofi", the head alone 

 persisting to complete the metamorphosis. 



Fig. 30. 



6. Another division process is that of splitting of the mass. This is 

 illnstrated by tlie case of the optic mass 



of the lobster (Figure 30), wliich splits 

 into an outer and an inner part. Com- 

 pare the origin of the nervous system of 

 Peripatus, K. &: H., Fig. 442, B. 



7. Under the second head, fusion of 

 contiguous masses, we may place such 

 cases as that of the union of indepen- 

 dently arisen ganglionic masses, such as 

 Mf)rgan describes for the Pantopod, Pal- 

 lene (Figure 31). Fig. 31. 



Fig. 30. Sections through three stnges in the development of the compound 

 eye of the lobster after G. H. Parker. In B and C the mass is seen to be splitting 

 into the retina and optic ganglion. See K. & H., Fig. 263. 



Fig. 31. Ventral part of sections across Pallene embryos. A, earlier stage, 

 showing the paired neural invaginations ; B, later stage, ganglia fused. See K. & H., 

 Figs. 409, 410. 



