John P. Munson 333 



This theory of the permanence of the reticulum of the nucleus and 

 cytoplasm, about which there seems to be some difference of opinion, is 

 siipported by the facts observed in this egg regarding the permanency 

 of the attraction sphere and cytocenter and the resulting polarity of 

 the egg. 



The Reticulum. — There is certainly good reason to be skeptical re- 

 garding the permanency of this reticulum, and consequently of its real 

 morphological value. Eeagents are often held responsible for its arti- 

 ficial production. To test the possible effects of reagents in this regard, 

 I have made permanent preparations, by the ordinary histological meth- 

 ods, of the striated muscle of an 'insect larva, in which the longitudinal 

 fibers and the transverse striations in their minutest details are beauti- 

 fully shown. On examining the living larva with the same magnifying 

 power, I found that I could see every detail about as plainly in the liv- 

 ing contracting muscle. These details in the living muscle were not 

 altered in the least in the prepared material except that the fibers and 

 their verrucosities were made more conspicuous. 



The Centrosome. — The regular arrangement of the microsomes and 

 radial fibers, immediately surrounding the centrosome in the resting 

 state, points to a primitive and permanent architecture in the midst of 

 this complex system of fibrils. In my work on the egg of Limulus, 6i, 

 I came to the conclusion that the vitalline-body in that egg is a direct 

 continuation of the centrosome of .the dividing oogonia, just as I have 

 been forced here to believe that the cytocenter in the later stages of the 

 egg of the tortoise is a continuation of the centrosome of the dividing 

 oogonia. Wilson, 84, has intimated that these bodies, like ordinary 

 yolk-nuclei, may be the result of metabolic activity of the nucleus, and 

 that the entire cytoplasm may be derived from the germinal vesicle. 

 The evidence of continuity of the cytocenter with the centrosome is 

 more conclusive in the egg of the tortoise, and it is, furthermore, so 

 radically different from the yolk-nucleus as previously described, that it 

 seems rash to insist on any identity between the two. I can readily 

 admit that so much of the facts as could be shown in the plates of my 

 work on Limulus was not sufficient to establish such a vital point, and 

 that even all that I could gather in four years of continuous study of 

 that egg was not equal to the amount of labor expended. In a pro- 

 longed study of this kind, one naturally, I suppose, forms certain gen- 

 eral conclusions which cannot be gained from a mere inspection of the 

 plates. Yet, what is evidently needed is positive, not negative evidence 

 of normal not abnormal or pathological conditions. 



