240 



TREADWELL. 



from the ordinary pigment of the rest of the cell, but containing 

 granules of a faint yellow color, agreeing in this respect exactly 

 with the prototroch band of the normal trochopore. In this 

 embryo there is, then, not merely a differentiation without cleav- 

 age of cilia, but of the charac- 



o 



teristic protoplasm accompanying 

 these cilia or, in other words, 

 we have here, in the unsegmented 

 embryo, not merely a differentia- 

 tion of cilia, but a differentiation 

 of prototrocli cilia. Later, fused 

 masses like those just described 

 are apt to break down, setting 

 free the ciliated fragments, and 

 by the twentieth hour the culture 

 will be swarming with ciliated fragments derived from this source 

 and from the breaking away of the " dwarf' described above. 

 These, of course, have not even a superficial resemblance to nor- 

 mal embryos. 



Fusion phenomena are rare in Podarke as compared with 



Cluetoptcrits, the largest fused masses I have found containing 



1 IG. 12. Unsegmented embryo 

 formed by fusion with well -differen- 

 tiated band of cilia. Living material. 



not more than six eggs. 



SUMMARY. 



1. After treatment with 2 }< nKCl solution, eggs of Podarke 

 obscitra exhibit various cleavages and pseudo-cleavages. 



2. The pseudo-cleavages involve only the cytoplasm and not 

 the nucleus, and have no resemblance to the normal cleavages. 



3. The cleavage involves both nucleus and cytoplasm, and 

 may give rise to a ciliated embryo. The cleavage in this case, 

 however, does not resemble the normal. 



4. Ciliated embryos may arise without cleavage. The differ- 

 entiation may be carried very far in such cases. This is espe- 

 cially noticeable in the character of arrangement of cilia. 



5. Fusion of embryos may occur, but in the solution men- 

 tioned, much fewer cells unite than in, r. g., CJicstoptcrns. 



MARINE BIOLOGICAL LABORATORY, 



WOODS HOLE, MASS., Sept. 5, 1902. 



