THE ECTOPLASM 



While the ectoplasm of the Protozoa has been well known 

 for years, that of eggs has not been generally recognized, 

 albeit eggs from every phylum in the animal kingdom either 

 have been described as showing ectoplasm or can be shown 

 to possess such. Since here we are concerned primarily 

 with eggs, it is necessary to review in detail the evidence 

 with respect to their ectoplasmic differentiation. 



The terms, exoplasm and endoplasm were first used by 

 Haeckel to describe the outer and inner cytoplasmic regions 

 of the sponge egg. In his monograph on the sponges 

 referred to at the beginning of this chapter, he speaks of the 

 hyaline exoderm (exoplasma) and a granular endoplasm 

 sharply set off from it. Metschnikoff^ in describing 

 eggs of a sponge emphasized its changes as due to amoe- 

 boid processes of the surface-cytoplasm. Gatenby^ has 

 described the ectoplasm of the sponge egg as follows: 

 (Fig. 5). 



Even in the youngest oocytes one may notice that at an 

 early stage a clear ectoplasmic zone becomes differentiated 

 from an inner or endoplasmic zone. The ectoplasmic zone 

 contains few or no vacuoles, is smooth, and is often drawn 

 out in the form of blunt pseudopodia or filamentous dendri- 

 form threads. The inner or endoplasmic zone is vacuolated 

 completely and has a fine, frothy appearance; it is in this 

 region that the cytoplasmic inclusions lie, granules in the 

 ectoplasm of the oocyte being rare or never found. Occa- 

 sionally, in preparations fixed in mixtures containing alcohol 

 or acetic acid, the vacuoles collapse, and the egg comes to 

 have a curious radiation of fibres around the nucleus (see 

 Joergensen's figures 8a). Eggs treated with silver nitrate 

 solution show the endoplasm browner than the ectoplasm. 

 ... In favourable cases not only young oocytes, but 

 amoebocytes, may be seen to possess ectoplasmic and 

 endoplasmic zones. As in the case of the older oocyte, the 

 cytoplasmic inclusions lie in the endoplasm, while the 

 pseudopodia consist mainly of ectoplasmic material. 



^ Metschnikoff, I.e. 

 -Gatenbv, 1919. 



8g 



