THE ECTOPLASM 



noted. (Fig. 6 and Fig. 7.) Kowalewsky^ without naming 

 the two regions gave a very clear description of them as 

 found in several ctenophore ("comb-jelly") eggs. Sub- 

 sequently, authors have confirmed Kowalewsky,^ often 

 only repeating the words of this great observer. Says 

 Agassiz: 



The yolk mass of the eggs of Idyia (and all Ctenophorae) 

 consists (after they are laid) of two layers, an inner yolk 

 mass more or less fatty, made up of large, irregular spheres. 

 This inner yolk mass is surrounded by a second thin, 

 outer layer, finely granular. This outer layer and its 

 enclosed central mass perform very different parts in 

 the development of the embryo, and it is of the utmost 

 importance to keep the changes these two layers undergo, 

 clearly distinct, while following the development of the 

 young Ctenophore. The outer layer as has been shown by 

 Kowalewsky, is eminently the embryonic layer, while the 

 inner mass acts as a mere nutritive yolk mass. 



FoF also described ecto- 

 endoplasmic differentiation in 

 Coelenterate eggs, using the 

 term, ectoplasm, instead of 

 Haeckel's exoplasma. Perhaps 

 the most striking ectoplasmic 

 structure described in eggs is 

 that found in the Beroe-egg 

 noted first by Chun and later Fig. 7. — Egg of a ctenophore, 



by YatSU.^ The ectoplasm in ^-^^/''^^'^''^ (^fter Kowalewsky). 



this egg is of a bright green colour, a fact that one 



^ Kozvalezvsky, 1866; iSy^. See also Kowalewsky and Marion, 

 1883. 



^ Agassiz, iSj^. 



' Fol, 1873. 



^ Chun, 1880; Yatsu, 190J. For other observers on the ectoplasm 

 of Coelenterate eggs see: Metschnikoff, 1886; Ziegler, i8g8; Appelof, 

 igoo; Hargitt, 1904; Spek, 1^26; Conklin, Cam. Publ., 103; 

 Ciamician, i8'/g; Korotneff, i88q; Harm, 1903; Maas, igoS; 

 Torrey, igoy; Komai, ig22. 



91 



