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SCIENCE 



[N. S. Vol. XXIX. No. 741 



growth period the chromosomes become aggregated 

 into a mass and the latter assumes a more or less 

 close connection with the nucleolus. Both nu- 

 cleolus and chromosome-mass are typically close 

 to the nuclear wall. Maturation proceeds to the 

 metaphase in the ovarian egg. A single instance 

 was observed where the mitosis had passed to 

 anaphase. The later phases of maturation occur 

 only after the egg is extruded and fertilized. The 

 nucleolus disappears during the metaphase of the 

 first maturation mitosis. It seems to contribute 

 a small amount of chromatin to the chromosomes, 

 after which its main bulk is resorbed by the cyto- 

 plasm. The nucleolus appears to be of the nature 

 of reserve food material rather than a waste 

 product. 



The astral system of the first mitosis consists 

 of a large, very chromatic centrosome surrounded 

 by a homogeneous acroplasmic centrosphere 

 which is bounded by a " microsome circle " and 

 an outlying astrosphere. Between metaphase and 

 anaphase in the free eggs the centrosome disap- 

 pears. The centrosphere of the second polar 

 spindle, as also of the fertilization and early 

 segmentation spindles, is achromatic and granular. 

 The centrosome appears to be merely an accom- 

 paniment of the astral system, representing a 

 transient metabolic phase of maturation coin- 

 cident with the formation of the first polar 

 spindle. The reduced number of chromosomes is 

 eighteen. The second mitosis segments univalent 

 chromosomes transversely and is the reducing 

 division. 



The Oerm-oell Determinants of Chrysomelid 

 Beetles: R. W. Hegneb, University of Michigan. 

 The Qerm-cell Determinants. — This paper is 

 based on the study of the lineage of the germ- 

 cells of Oalligrapha multipunctata and three other 

 chrysomelid beetles. At the time of laying a disc- 

 shaped mass of granules is present at the posterior 

 end of the egg suspended in the peripheral layer 

 of cytoplasm. I have called this disc the " pole- 

 disc" and the granules the "germ-cell deter- 

 minants." The cleavage products in the eggs of 

 these beetles migrate through the central yolk 

 mass to the periphery, where they produce the blas- 

 toderm. Those cleavage products that come in 

 contact with the germ-cell determinants do not pro- 

 duce blastoderm cells, but continue their migration 

 until they are entirely separated from the egg. 

 These cells take with them practically all of the 

 germ-cell determinants. At first there are 16 of 

 these cells, but they soon divide twice, the final 

 number being 64. These are the primordial germ- 



cells. They can be traced back into the embryo, 

 where by amoeboid movements they migrate half 

 to either side of the germ-band. Later they pro- 

 duce the germ-glands. The sexes can be distin- 

 guished during the embryonic period by the shape 

 of the germ-glands. 



The Results of Removing the Oerm-oell Deter- 

 minamts. — ^A number of fresh eggs were punctured 

 and the germ-cell determinants allowed to fiow 

 out. These eggs developed into embryos or larvse 

 which contained no germ-cells. 

 The Sexual Differences of the Chromosom,e Growps 

 in Pyrrochoris and Syromastes: Edmund B. 

 Wilson, Columbia University. 

 The facts in Pyrrochoris and Syromastes have 

 been supposed to contradict the general rule, estab- 

 lished for many other forms, that those sperma- 

 tozoa which receive the accessory chromosome are 

 female-producing, the others male-producing; for 

 in both cases the two sexes have been described 

 as having the same number of chromosomes — 24 

 in Pyrrochoris and 22 in Syromastes. A reexam- 

 ination of both sexes in the two forms has proved 

 that they form no exception to the rule, previously 

 published accounts being erroneous in respect to 

 the male of Pyrrochoris and the female of Syro- 

 mastes. 



In Pyrrochoris the male number is not 24, but 

 23, the odd or accessory chromosome being the 

 largest of the chromosomes. Half the spermatozoa 

 receive this chromosome and half fail to receive it, 

 the former class having 12 chromosomes and the 

 latter li. The female groups contain 24 chromo- 

 somes, of which two are of the same relative size 

 as the single accessory of the male. Pyrrochoris, 

 therefore, conforms precisely to the usual type 

 shown in Anasa, Protenor, etc. 



In Syromastes the male number is 22 (as de- 

 scribed by Gross), but the female number is not 

 22, but 24, as was first inferred by the writer 

 from the condition seen in the male only. Direct 

 observation has now proved that this inference 

 was correct. Syromastes constitutes a new type 

 in which there are two accessory chromosomes 

 (the second and third smallest of the spermato- 

 gonial groups) which pass together, as a bivalent, 

 into half the spermatozoa. These spermatozoa 

 receive 12 chromosomes, the others 10, and the 

 somatic numbers of the sexes prove that the 

 former class are female-producing, the latter male- 

 producing. (Demonstrations by photographs.) 

 Some New Types of Chromosome Distribution and 

 Their Relation to Sex: Febnandtjs Patne, 

 Columbia University. 



