20 Hjalmar Théel, 



profile a row of such cells looks like a low palisade, the sides of each 

 being flattened where they touch ; the outer end of the cells is slightly 

 convex, while the inner is more sharply and irregularly curved, thus 

 making the inner surface of the blastoderm rather uneven. Seeing 

 that the cells are not by any means regular in shape, some being 

 shorter, broader and evidently in a state of division and multiplication, 

 as may be seen from the different stages of karyokinesis, this uneven- 

 ness becomes very conspicuous. The chromatic filaments or chromosomes 

 in those cells which are in a state of division, appear very clearly if 

 the whole larva be stained with Grubler's acetic acid carmine. It is not 

 yet possible to distinguish any thickened area in the blastoderm. 



Soon the Blastosphere begins to rotate, first feebly and then more 

 rapidly, by means of the plasmatic hair-like processes or cilia, which 

 protrude, reach a considerable length and move more or less rapidly 

 in the intermediate space between the larva and the vitelline mem- 

 brane, PL II, fig. 36. Sometimes I have found that the mucilaginous 

 coat which surrounds the vitelline membrane of the ^g^, still remains 

 enveloping the whole. However, the larva now in a short time escapes 

 from the enveloping coats of the egg into the water and begins to swim 

 about, PI. II, fig. 33—35. 



Simultaneously an obvious differentiation begins to take place in 

 the cells at the vegetative pole, which increase in length and become 

 higher and columnar, those at the opposite pole on the contrary still 

 remaining for a short time unchanged. Besides the cilia, the outward 

 ends of the cells of the blastoderm possess extremely minute, closely 

 crowded plasmatic processes, PL III, fig. 51, which treated with osmic acid 

 present themselves distinctly. I never saw anything similar to this before. 



After this the Blastula begins to extend in length and increase 

 in such a degree, that at about twelve or thirteen hours after the fecun- 

 dation it reaches a length of 0,i5 mm. and a breadth of 0,09 mm. In 

 many places the cells are in a state of division, presenting the charac- 

 teristic chromatic filaments in different positions. 



Gradually the Blastula changes its external shape, so that it al- 

 most assumes a cylindrical form and reaches an unusual length. The 

 largest I have observed, PL 11.^ fig. 35., which were about twenty hours 

 old and fully mature, had a length of 0,2 mm. and a breadth of 0,ii mm.; 

 other larv£e, in which the first indication of an invagination at the vege- 

 tative pole was making its appearance, measured 0,23 mm. in length, but 

 only 0,044 mm. in breadth, PL II, fig. 34. 



