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separation of the blastomeres leads to the production of two quite 
separate and independent twins of half the normal size (fig. 1; A, 
normal gastrula; B, half-sized gastrula). Each of the isolated blasto- 
meres undergoes a cleavage like that of a normal ovum (not a half- 
cleavage) gives rise to a blastula of half the usual size but otherwise 
normal, undergoes a normal gastrulation and develops into a typical 
metameric larva which even at the end of two days (at a stage ap- 
proximately like HarscHex’s Fig. 67) differs in no wise, except in size, 
from the normal forms. Incomplete separation of the two blastomeres 
gives rise to double embryos of many varieties, which form a com- 
plete series leading from scarcely bilobed forms to those in which 
two nearly perfect bodies are joined by only a narrow bridge of tissue. 
The double embryos develop into segmented free-swimming larvae but 
rarely live beyond the first twenty-four hours. 
Experiments with 4-celled stages gave analogous results but de- 
velopment never continued long after the closure of the blastopore 
and the first appearance of metamerism. (1) If the four blastomeres 
be completely isolated, each may give rise to a dwarf blastula, gas- 
trula, and oval free-swimming larva, one fourth the normal size but 
