206 



INTERNAL FACTORS 



IV. i 



organ, but without an archenteron, while from the remaining 

 twelve is derived a ciliated embryo with a large sol id archenteron, 

 but destitute of an apical organ and lappets. 



Wilson asserts that the size of cells in partial is the same as 

 in total larvae ; their number appears to be proportional to their 

 germinal value. 



From fragments of blastulae normal, or nearly normal, dwarf 

 Pilidia may arise, but the degree of development again depends 

 on the origin of the fragment. While the lower third becomes 



FIG. 116. Cerebratulm. Larvae from portions of the 8-cell stage. 

 A, B. Larva from lateral 4-cell group. Note presence of both apical 

 organ and archenteron. C. Similar, but younger. D. Larva from upper 

 quartette plus two cells of lower quartette. Note that there are three 

 apical organs, a large blastocoel, a small archenteron, and two in- 

 vaginations of ectoderm at the sides of the archenteron. (After Zelenv. 

 1904.) 



a ciliated embryo without an apical organ, a piece of the upper 

 two-thirds developed (in one case) into a larva with a gut, with 

 two apical organs, but no lappets (Zeleny). Wilson states that 

 in Cerefoatulv* lacteus the archenteron is small in animal frag- 

 ments, the apical organ frequently, though not apparently always, 

 absent in pieces of the vegetative hemisphere. 



Animal fragments of the blastula have a greater total poten- 

 tiality, a greater regulative capacity, than the animal blastomeres 



