The Cytoplasm of the Sea Urchin Egg 



147 



are located around the Golgi zone. They are revealed 

 by Baker's Sudan black method ( 1 ) and correspond 

 to the "lipochondria" of some workers (8). 



Epithelial cells contain an organelle, lying to one 

 side of the nucleus, with an ultra-structure similar 

 to that described for neurones (tig. 5). This organelle 

 is identified as the Golgi apparatus. 



When the above results are considered alongside 

 previous work (4, 3, 6, 9, 10) it would appear that the 

 Golgi apparatus is a distinct type of organelle, 

 morphologically well defined, which exists in the 

 cells of animals belonging to such diverse classes as 

 mammals and gastropods. In all probability, there- 

 fore, it is a universal constituent of animal cells. 



I am greatly indebted to Dr. V. E. Cosslett for the use 

 of the Siemens Elmiskop I at the Cavendish Laboratory, 

 Cambridge, and to Mr. R. Home of that Laboratory for 

 his most skillful assistance in the examination of speci- 

 mens. 



Reference.s 



1. Bakir, J. R., Qiiort. J. Microscop. Sci. 85, 1 (1949). 



2. Bkamhii I , F. W. R. and Gatenby, J. B., Proc. Roy. Soc. 



Diihliii 17, 275 (1923). 



3. Dai ION, A. J. and Fhlix, M. D., Am. J. Anal. 94. 171 



(1954). 



4. Gatenbv, J. B., J. Roy. Microscop. Soc. 74, 134 (1954). 



5. Gati-nhy, J. B. and Bfams, H. W., The Microtomists' 



Vadc MccLim. Churchill, London, 1950. 



6. Lacy, D. and Challice, C. E., /// Mitochondria and 



other Cell Inclusions. S.E.B. Symposium, Oxford, 

 1955. 



7. Palade, G. E., J. E.xpll. Med. 95, 285 (1952). 



8. RoQUE, A. L., /. Roy. Microscop. Soc. 74, 188 (1954). 



9. Sjostrand, F. S. and Hanzon, V., Exptl. Cell Research 



7, 415 (1954). 



10. , E.xpcrieiilia. 10, 367 (1954). 



I 1. Thomas, O. L., Quart. J. Microscop. Sci. 88, 445 (1947). 



Basophilic Structures in the Cytoplasm of the Sea Urchin Egg 



B. A. Afzelius 



The Laboratory for Biological Ultrastnicture Research of the Department of Anatomy, Karoliiiska Inslitiitet, and the 



Wenner-Gren Institute for Experimental Biology, Stockholm 



The sea urchin egg is an ideal subject for a study of 

 the microscopic and submicroscopic organization 

 of the nucleic acids. The nucleic acid content in the 

 egg is high, giving the cytoplasm an intense baso- 

 philia, especially in the young oocyte (4). The visco- 

 sity of the egg cytoplasm is low, permitting a rather 

 complete stratifying of the cell components within 

 the intact egg by centrifugal methods (9, 10), and 

 thus furnishing a means of comparing the submicro- 

 scopic appearance of cytoplasmic fractions with their 

 light microscopic staining properties. 



This paper is a preliminary report of an electron 

 microscopical study of some of the nucleic-acid- 

 containing structures in the sea urchin egg. Eggs of 

 the species Echinus esciilentiis, Psainniechiniis tuilia- 

 ris, and Strongylocentrotiis droehachiensis were used. 



The microscopically detectable basophilic elements 

 were investigated in f^xed material by the Feulgcn tech- 

 nique, methyl green-pyronin staining controlled by ribo- 

 nuclease-treated sections (5), gallocyanin-chromalun 

 staining (7) and other techniques considered to be less 

 specific for nucleic acids. The fixation fluid used for most 

 of the experiments was Carnoy's fluid, as no loss of the 

 nucleic acids occurs following this fixation (17). However, 

 since cytoplasmic fixation in Carnoy's fluid was rather 

 poor, comparison tests were performed on material 

 fixed in osmium tetroxide, formaldehyde, Regaud"s fluid, 

 or Bouin's fluid. Also eggs that were vitally stained with 

 toluidine blue were studied in the living condition and 

 in sectioned material fixed according to the method of 

 Izquierdo (14). The electron microscopical part of the 

 work was performed with the sectioning technique 



according to Sjostrand (19) after fixation in 1 per cent 

 osmium tetroxide in sea water (2). An RCA EMU 2c 

 electron microscope was used. 



Light microscopical observations. — Feulgen stai- 

 ning gave a negative result with regard to both the 

 pronucleus of the egg and the different strata of the 

 centrifuged egg. Similarly, there were no detectable 

 methyl green staining of sea urchin eggs with the 

 methyl green-pyronin technique. 



Staining methods for ribonucleic acid (RNA) loca- 

 lization on the other hand indicated the presence of 

 appreciable amounts of RNA in the egg cytoplasm. 

 When centrifuged eggs were studied, the cortex 

 (which is not affected by centrifugation) and the 

 layers of clear cytoplasm and mitochondria were 

 found to contain the bulk of the ribonucleic acids. 

 Also, in the bottom of the mitochondrial zone, 

 which in the eggs examined was the heaviest one, 

 there were particles with a size ranging from 0.8 to 

 3 //, which stained readily with the RNA-specific 

 stains. Other particles of similar size and staining 

 characteristics did not move to the centrifugal pole 

 of the eggs but remained apparently attached to 

 the outer surface of the nuclear membrane. Similar 

 results were obtained by vital staining with toluidine 

 blue. The clear la\er, the layer of heavy bodies at 

 the bottom of the egg and the bodies attached to the 

 nuclear membrane all stained intensely, the two 

 layers being sharply delimited. However, the mito- 



