3^5 Erste Sektion: Cytologie und Protozoenkunde. Erste Sektion. 



It seems highly important that we should learn to distinguish 

 between metaplasm (archoplasm, yolk-nucleus and all such amor- 

 phous protoplasmic inclusions which serve as food), and the 

 structurally formed living substance represented by the centro- 

 some and aster. 



That the centrosome and aster may persist in the growing 

 ovarian egg is doubted by some, who seem not to have studied 

 the matter very thoroughly. They seem to find no difficulty in 

 admitting the persistence of the centrosome in the sperm cell, 

 the middle piece bf which is often said to form the centrosome 

 of the male pronucleus. 



I have shown 1 ) that, in Papilio rutulus, the centrosome of 

 the spermatogonia persists as the head piece of the Spermatozoon 

 fig. 13, 14, pl. Ic. 



If it be admitted that this cytoplasmic structure may per- 

 sist in the sperm cell throughout its many striking changes, and 

 then after its maturity, valid reasons should be given for refusing 

 assent to the suggestions, — which microscopic preparations af- 

 ford so abundantly, — that the centrosome and aster found in 

 the growing ovarian egg is a direct continuation of the centro- 

 some of the dividing oogonia. 



I have shown that in the butterfly the Nebenkern of the 

 sperm cell has a nuclear origin, being a remnant of the spindle, 

 and that it is a temporary protoplasmic inclusion like the yolk- 

 nucleus in Limulus (not the vitelline body), and the similar but 

 more striking bodies in the egg of the tortoise. I have shown 

 that the centrosome is entirely distinct from the Nebenkern which 

 is gradually absorbed as food material. As the Nebenkern of the 

 sperm seems to consist of a substance very similar in appearance 

 to the metaplasm or yolk-nucleus of ovarian eggs, they are pro- 

 bably much alike, the one being a remnant of the spindle in the 

 maturation division, the other a product of the chromatin or ex- 

 truded caryolymph united with proteid food substance. If the 

 nucleus be forced into the cytoplasm by pressure, it presents the 

 appearance of a Nebenkern. By such pressure, the chromatin in 

 the form of spherical chromosomes or a nuclear reticulum as- 

 sumes, under the microscope, the appearance of archoplasm. We 

 thus have a basis for understanding the similarity in appearance 

 of the yolk-nucleus, archoplasm, metaplasm and Nebenkern in 

 sperm cells and in egg cells. Endless confusion is apt to arise when 

 we fail to distinguish these amorphous bodies in the cell, from 

 the formed structures in the cytoplasm represented most clearly 

 in the centrosome and aster. 



*•) M u n s o n : Spermatogenesis of Papilio rutulus. (Proceedings Boston 

 Society of Natural History, 33, No. 3.) 



