232 



SCIENCE. 



[N. S. Vol. V. No. 110. 



scure. They have been recently found and 

 studied in the cells of the spinal and sym- 

 pathetic ganglia of the frog (Lenhossek, Deh- 

 ler), in the neuvochord cells of an annelid 

 ( Miss Lewis ) and in ganglion cells of a snail 

 (McClure). They have also been found in con- 

 nective tissue cells, pigment cells, resting 

 leucocytes, etc. In the great majority of nou- 

 dividing cells, however, they have not been 

 demonstrated. 



It would appear, from the observations given 

 above, that the centrosome and sphere may 

 have some other function in the economy of the 

 cell, in addition to their important role in the 

 process of caryokinesis. In the case of the 

 ovarian stroma the facts presented appear to 

 favor the view that the centrosome, as such, is 

 not a permanent organ of the cell, but may ap- 

 pear and disappear according to the conditions 

 which prevail in the life of the cell. 



C. M. Child. 



rv. THE CENTEOSOMES IN THE ANNELID EGG. 



My observations have been made on the ma- 

 rine annelid Chsetopterus in the endeavor to 

 throw light on the following open questions : 



1. Is there in the egg a definite structure — 

 centrosome — not an artifact, and not identical 

 with the ' centrosphere' or ' astrosphere' ? 



2. Is the centrosome ' a derivative structure 

 arising by a modification of some pre-existing 

 element in the cell,' or is it 'a permanent and 

 ultimate organ of the cell, an organ sui gene- 

 ris, and coexistent with other ultimate organs 

 of the cell, as the nucleus and the cytoplasm' ? 



3. Do the centrosomes grow, multiply by self- 

 division, and persist from one cell generation to 

 another, or are they formed anew in each cell 

 in anticipation of caryokinesis ? 



4. What r61e does the centrosome play in 

 fecundation — ' its bearing on the phenomena 

 of inheritance' ? Is there a union of male and 

 female centrosomes during fecundation similar 

 to that of the male and female pronuclei — a 

 ' quadrille of the centers' ? 



5. Whence come the centrosomes of the first 

 and succeeding cleavage spindles ? 



6.' What is the relation of the centrosome to 

 the centrosphere (astrosphere) ? To the cytoplas- 

 mic rays and network ? To the Zwischenkorper ? 



If the eggs are kept in sea water for half an 

 hour or more and not fertilized, all except the 

 smaller ovarian eggs are found to have the first 

 maturation spindle well formed, in its definitive 

 position, and always in the same stage of de- 

 velopment, i. e., the metaphase or equatorial- 

 plate stage. But if the eggs are preserved 

 after having remained only a few minutes in 

 sea water they are all, so far as my experience 

 goes, found to contain the germinal vesicle and 

 no spindle. I infer from this that sea water in 

 some way stimulates the egg to the production 

 of maturation spindles. 



The smallest ovarian eggs are characterized 

 by their relatively large nuclei and by their 

 compact cytoplasm, which, devoid of yolk, 

 stains a deep purple with our method — iron- 

 alum hsematoxylin and orange G. I can find 

 in such eggs nothing resembling or indicating a 

 centrosome. 



Yolk granules which stain yellow soon begin 

 to accumulate in the cytoplasm and the eggs 

 grow larger. The yolk, however, is not at first 

 distributed uniformly throughout the cyto- 

 plasm, but is most abundant near the periphery 

 of the egg and frequently also immediately 

 outside the nucleus. Where the yolk is present 

 one can readily distinguish a cytoplasmic net- 

 work, in the meshes of which yolk is held. 

 The threads of the network have the appear- 

 ance of minute granules arranged in linear 

 order. They form a sort of membrane at the 

 periphery of the egg, and are continuous with 

 the nuclear membrane. 



But up to the time when the egg has attained 

 about two-thirds its full size there remain 

 masses of cytoplasm containing no yolk and 

 consisting of a network closely compact and 

 staining dark purple. The component threads 

 of these cytoplasmic masses are evident enough, 

 and are continuous with the rest of the cyto-re- 

 ticulum. These masses I consider to be equiva- 

 lent to the nebenkerne or paranuclei of authors. 

 They vary in shape and number in different 

 eggs and at different stages of development, 

 now appearing as one or two crescentic masses 

 about the nucleus, and now broken up into 

 many pieces. Their fate is always the same ; 

 they gradually fray out and become resolved 

 into the general cyto-reticulum. 



