578 PATTERNS AND PROBLEMS OF DEVELOPMENT 



ever, that isolated 1/2 blastomeres gave rise to complete or only slightly 

 defective larvae. Cleavage of isolated blastomeres as halves was recog- 



D E 



Fig. 182, ^-£.— Cleavage stages of Siyela partita. A , fertilized, undivided egg, lateral view; 

 yellow crescent indicated by broken line; clear protoplasm at its borders, by dotted line. B, 

 eight-cell stage in lateral view; yellow crescent indicated. C, apical, D, basal, view of sLxteen- 

 cell stage; boundary of yellow crescent indicated. E, early gastrula; neural plate cells indi- 

 cated by dotting; notochord, by vertical lines; mesenchyme, by oblique lines; muscles, by hori- 

 zontal lines; partially invaginated entoderm and general ectoderm, white (after Conklin, 19050). 



nized by Crampton (1897), but he also beheved that whole larvae resulted. 

 Chabry was later confirmed by Conklin,"" who followed the cell lineage of 



" Conklin, 1905c, 1906, 191 1 ; experiments on Styela partita, Ciona iniestinalis, Molgiila man- 

 hattensis, and Phallusia mammillaia. 



