382 



SCIENCE. 



[X. S. Vol. XXI. No. 532. 



graphs of Living Eggs by Katharine 



Foot and Ella C. Strohell: Edwin G. 



CoNKLiN, University of Pennsylvania. 



Three very different kinds of protoplasm 

 may be observed and photographed in the 

 living ovocytes and nnsegraented eggs of 

 Cynthia partita; these are the yellow meso- 

 jjlasm which later enters into the meso- 

 derm, the gray endoplasm which gives rise 

 to the endoderm, and the transparent ecto- 

 plasm which becomes ectoderm. Three 

 additional differentiations are visible and 

 have been photographed before or imme- 

 diatel}' after the first cleavage, viz., the 

 mesoplasm is differentiated into a deep 

 yellow substance, the myoplasm, which 

 gives rise to the muscles of the larva and 

 into a light yellow material, the chymo- 

 plasm, which becomes mesenchyme; there 

 is also recognizable an area of light gray 

 material, the chorda-neuroplasm, which 

 develops into the chorda and neural plate 

 of the larva. 



As early as the close of the first cleavage 

 all of these substances are localized in the 

 egg in positions corresponding to those 

 which they will occupy in the embryo or 

 larva ; the mesoplasm forms a yellow cres- 

 cent around the posterior side of the egg 

 dorsal to the equator, the chorda-neuro- 

 plasm takes the form of a gray crescent 

 around the anterior half of the egg, the 

 endoplasm lies between these two crescents 

 at the dorsal (vegetal) pole of the egg, the 

 ectoplasm occupies the ventral (animal) 

 hemisphere. The dorsal border of the yel- 

 low crescent consists of light yellow proto- 

 plasm (chymoplasm), which gives rise to 

 the mesenchyme of the trunk, while a sim- 

 ilar area of light yellow or clear chymo- 

 plasm lies at the middle of the crescent 

 behind and ultimately forms the caudal 

 mesenchyme of the larva. All of these 

 areas and substances can be followed with 

 ease and certainty throughout the develop- 

 ment until they enter into the principal 



organs of the larva, a fact which is beauti- 

 fully shown by the photomicrographs. 



Experimental Studies on the Ascidian Egg: 

 Edwin G. Conklin, University of Penn- 

 sylvania. 



That the various areas and substances of 

 the ascidian egg are actually organ-form- 

 ing ones may be demonstrated by experi- 

 ment. Operations on the unsegmented egg 

 inhibit development, but when certain blas- 

 tomeres of the cleavage stages are killed 

 or injured the ensuing development of the 

 uninjured blastomeres is strictly partial ; 

 in no case do such blastomeres give rise to 

 other organs than those which they would 

 have produced under normal conditions. 

 Conversely, if the cells which contain the 

 myoplasm are destroyed the resulting larva 

 has no muscle cells; if the cells containing 

 the chorda-neuroplasm be removed there 

 will be no chorda nor neural plate in the 

 resulting monster; the same is also true of 

 the ectoplasm and endoplasm. 



Since all these substances are divided 

 bilaterally at the first cleavage, each of the 

 first two blastomeres contains one half of 

 all of the organ-forming substances, and 

 inasmuch as isolated blastomeres of the 

 ascidian egg prodiace rounded masses of 

 cells which tend to close over the injured 

 part, it frequently happens that the half 

 embryo or larva bears a superficial resem- 

 blance to a whole one ; however, a study of 

 their cell-lineage and later development 

 shows that they are still half embryos and 

 larva?. When the egg is injured along any 

 other plane than the median one nothing 

 even remotely resembling a normal larva is 

 ever produced. 



Prophases of the First Maturation Spindle 

 of Allolobophora foetida: Katharine 

 Foot and E. C. Strobell. 

 At the end of the growth period, the 



chromatin granules which are distributed 



