
918 The American Naturalist. [October, 
form of Daphnide undergo different types of cleavage, one being 
holoblastic and the other meroblastic, the difference being probably 
produced by the amount of food yolk; the summer eggs belong 
to the regular holoblastic type of cleavage; and the winter egg to the 
meroblastic type, showing a close resemblance to the ova of some 
insects.” 
The author’s view as to the mechanism of karyokinesis is explained. 
The conclusion is based largely on a study of karyokinesis in the squid 
and starfish, and the author believes this same explanation may apply 
to the whole phenomena of cell divisions, the essential point of the 
theory being that the ‘“‘archoplasmic filament’’ radiates from two 
centers on opposite sides of the eggs penetrate the cell membrane, 
flattening the chromosomes into a plate, the radiating fibers (archo- 
plasmic filaments), continuing to push, break up the plate into two 
portions, driving each in the opposite direction,—#.e., away from the 
archoplasmic spheres. The bilaterality of the egg of the squid is the 
same as the bilaterality of the adult animal ; and the arrangement of 
the protoplasmic cap at the animal pole also shows well-marked 
bilaterality, corresponding to that of adult animal, 
The Regeneration of the Tail of Lumbriculus.’—Miss Ran- 
dolph has an abstract of her work on the growth of new tails in the 
Annelids. The new ectoderm arises by proliferation of the ectoderm 
around the line of fission. From this new ectoderm arises the ven-: 
tral nerve-chain and the dorsal sete. The new digestive tract is 
formed from the cells of the old. The most interesting fact is in the 
formation of the new mesoderm, which “is formed in great part 
from specialized cells in the region of the peritoneal epithelium of the 
ventral longitudinal muscles, on each side of the ventral nerve-cord, 
een it'and the ventral row of sete. These cells, which I propose 
to call neoblasts, are distinguished from the cells of the peritoneum 
by their great size and by the presence of acell body. They are to 
be found in every variety, with the possible exception of one or more 
at the anterior extremity, and represent the ‘chorda cells’ described 
by Semper in the Naids and Chetogaster. Very soon after the fission 
of the worm the neoblasts in the end somite begin to divide, and give 
rise to the greater part of the embryonic tissue that is afterwards differ- 
entiated into mesodermic structures. 
“ The neoblasts are to be regarded as specialized embryonic cells, 
set apart for the rapid formation of new mesodermic tissue immedi- 
3 Zool. Anz., No. 362, 1891. 


