March, 1920] GENETICS 89 



posthumous article, pointing out two facts which help explain conflicting results of echinoderm 

 crosses. First, whole eggs or egg fragments which have been taken and appear to have no 

 nuclei may contain chromatin of nucleus in irregular mass not recognizable in living proto- 

 plasm; and this chromatin is capable of normal participation in development. .Second, 

 nucleus may be divided into two or more partial nuclei, probably due to failure of chromosome 

 vesicles to coalesce at proper stage in reconstruction of nucleus. These two discoveries are 

 used to explain facts taken from literature and from new experiments. Egg fragments of 

 Sphaerechinus apparently without nuclei, fertilized by sperm of Paracentrolus (Strongylocen- 

 trotus), yielded some paternal larvae (as previously reported), but majority were intermediate 

 larvae. But intermediate larvae had large nuclei, hence were diploid, for author confirms 

 former conclusion that nuclear size is safe criterion of haploid or diploid number of chromo- 

 somes. Egg fragments in these cases must have contained nuclei. Disappearance of nucleus 

 on shaking occurs only in young eggs, probably just after polar-body formation. In fully 

 ripe female only few eggs are in this stage, while nuclei of older eggs resist disintegration on 

 shaking. One supposedly merogonous larva from Sphaerechinus X Paracentrolus (female 

 named first) was nearly paternal. It had smaller nuclei than genuine hybrids, but not small 

 enough to be haploid. Author concludes egg fragment contained only partial nucleus. Some 

 larvae of same cross were maternal, and these have been shown to be plainly haploid. In 

 one set of crosses Sphaerechinus X Parechinus (Echinus) many larvae died early; these were 

 probably haploid. Those that lived longer were probably not haploid, yet some were pater- 

 nal. However, crosses involving whole egg of Sphaerechinus are sometimes paternal. Sug- 

 gests that when "merogonous" larvae were paternal egg fragment contained partial nucleus, 

 and that these maternal chromosomes helped develop larva to pluteus stage at which paternal 

 characters could appear. Godlew r ski's merogonous Parechinus X Antedon crosses gave some 

 maternal embryos, but author suspects egg fragments contained nuclei; nuclear size was not 

 determined in these larvae. — Some larvae have nuclei of haploid size on one side, diploid size 

 on other. These are attributed to partial merogony, dispermy in which one sperm nucleus 

 fuses with egg nucleus, other functions alone. In partial merogonous larvae of crosses Sphaer- 

 echinus X Paracentrotus and Sphaerechinus X Parechinus diploid and haploid cells migrate 

 and mix, making certain characteristics intermediate. If two cleavage spindles resulting 

 from dispermy be placed, not parallel, but perpendicular to one another, all micromeres, and 

 hence mesenchyme, might be diploid. One merogonous larva appeared to be in this condition, 

 its gut and mesenchyme being diploid and its skeleton normal. Some doubtful cases are 

 described. — Author suggests two stages of development, early stage in which any chromosomes 

 will suffice for development, later stage in which right interchromosomal combination must 

 be present, as well as mutually compatible cytoplasm and chromosomes. Explains why 

 hybrids between Sphaerechinus and either Paracentrotus or Parechinus can be paternal only 

 when maternal nucleus is also present: maternal nucleus is necessary in order that develop- 

 ment may proceed into second stage when paternal characters can appear. Nucleus is not, 

 however, merely organ to insure development : giant eggs formerly shown, in crosses, to pro- 

 duce more nearly maternal embryos than did normal eggs in similar crosses owed that prop- 

 erty to their double nuclei. Moreover, hybrids from egg fragments were not less like mother 

 than were hybrids from whole eggs, as they would be if cytoplasm determined characters. — 

 A. Franklin Shull. 



601. Bridges, Calvin B. The genetics of purple eye-color in Drosophila melanogaster. 

 Jour. Exp. Zo6l. 28: 265-305. May 20, 1919. — Purple is an early mutation (found Feb. 

 20, 1912) that has proved especially useful. It is strictly recessive, easily and rapidly 

 separable from wild-type, fully viable, fertile, and productive. Its locus is in second 

 chromosome 6.2 units to right of black, or 52.7 to right of star. This is middle of second chro- 

 mosome as mapped, and apparently also in actuality, since this region is characterized by 

 abnormally high double crossing over, special sensitivity to action of age, heat, and cold upon 

 amount of crossing over, and by special limitation upon action of certain genetic crossover 

 variations. Purple has been involved in development of many important fields of Drosophila 

 genetics: with vermilion it gave '"intensification" or "disproportionate modification." It has 



