davenpoet: processes concebned in ontogeny. 



195 



Sacculina, where the thorax and abdomen are thrown off, the head alone 

 persisting to complete the metamorph 



Fig. 30. 



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

 illustrated by the case of the optic mass 

 of the lobster (Figure 30), which splits 



into an outer and an inner part. Com- ^^P*ijffi£fmj&&»^ 

 pare the origin of the nervous system of CL 

 Peripatus, K. & H., Fig. -142, B. 



7. Under the second head, fusion of 

 contiguous masses, we may place such 3- 

 cases as that of the union of indepen- 

 dently arisen ganglionic masses, such as 

 Morgan describes for the Pantopod, Pal- -s 



lene (Figure 31). Fig. 31. 



Fig. 30. Sections through three stages 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. .4. earlier staee, 

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

 Figs. 409, 410. 



