March 19, 1915] 



SCIENCE 



441 



The Orientation of the Nuclear Contents in the 



Motor Electric Cells of Torpedos: Ulric Dahl- 



GREN. (With lantern.) 



The nucleus contains, besides the usual chroma- 

 tin bodies, a large typical plasmosome and a some- 

 what smaller body, the para-nueleolus. These two 

 are always oriented in a dorso-ventral position and 

 the cause of this orientation was sought in either 

 the electric current that passes through the tissue 

 or in the influence of gravity. Electric currents 

 of the same strength as those generated by the 

 fish and when applied at right angles to or di- 

 rectly against the orientation in question failed 

 to influence it even when applied for several 

 hours. Stronger currents moved the nuclear eon- 

 tents, but also changed the structure and chemical 

 composition of the parts. One fact seemed to be 

 shown; that the plasmosome was not moved to 

 either pole of the nucleus, but assumed a position 

 between two materials that did occupy the two 

 halves of the nucleus. 



Gravity experiments were interesting and 

 seemed to solve the question; at a lower rate of 

 centrifugal force the plasmosome was moved to 

 the side of the nucleus away from the force. At 

 a higher rate the chromatin bodies were also 

 moved, while with the greatest force used the para- 

 nucleus was also moved. The Naples torpedos 

 possess no paranueleolus in these cells. 



Genetics 

 Bristle Inheritance in Drosophila: E. Caeleton 



MacDowell. (With lantern.) 



A race of Drosophila ampelophila has been es- 

 tablished from wild flies that has extra thoracic 

 bristles. Crosses with normal flies prove that the 

 extra bristled condition is a recessive Mendelian 

 character. The number of extra bristles that ap- 

 pear in this race varies. The first six generations 

 from parents selected for increase in bristle num- 

 ber showed a steady rise in the numbers of 

 bristles. For thirteen generations after this, se- 

 lection was apparently ineffective. 



Three interpretations of successful selection may 

 be examined. 



1. Determiners may be inconstant; higher 

 grades of a character have higher grade determin- 

 ers. This would not account for the thirteen gen- 

 erations of ineffective selection, nor the genetic 

 uniformity in the later generations which is evi- 

 denced by, (a) high and low grade parents from 

 the same family giving like offspring, (6) analysis 

 of high and low grades by crosses, (c) absence of 



correlation between means of parents and off- 

 spring in whole generations after the sixth. 



2. Selection may produce a more vigorous line, 

 and this vigor may occasion the better develop- 

 ment of the character. A large fly in the extra 

 race is apt to have more bristles than a small one. 



3. Multiple factors may exist which are reduced 

 to a homozygous condition by selection. Ex- 

 tracted extra bristles have a lower distribution 

 than the uncrossed extras, j'et the high extremes 

 of the selected race are equalled. This would be 

 the result if selection had removed some acces- 

 sory restricting genes. These facts do not agree 

 with the second interpretation, whereas all ob- 

 servations are in accord with the third interpreta- 

 tion. 



The Behamor of a Unit Character in the Grouse 

 Locust, Paratettix: Robert K. Nabours. 



Sise Dimorphism m the Spermatozoa and Its Ee- 

 lation to the Chromosomes: Charles Zelent 

 AND E. C. Eatjst. 



Further evidence has been obtained in favor of 

 the view that the size dimorphism of the sperma- 

 tozoa observed in several species by the authors 

 is correlated with the chromosomal dimorphism of 

 the spermatids. The ratio between the chromo- 

 somal volumes was calculated from published fig- 

 ures of the spermatogenesis in the three species, 

 Musca domestica, Alydus pilosulus and Anasa 

 tristis. From this ratio the expected ratio be- 

 tween the head lengths in the resulting sperma- 

 tozoa was calculated on the assumption that the 

 size of the heads is directly proportional to the 

 amount of chromatin received and on the further 

 assumption that the shape of the heads is the same 

 for all sizes. The calculated ratios and the cor- 

 responding observed ratios are as follows: Alydus 

 piZosMZMS, calculated 1.00:1.06, observed 1.00:1.055; 

 Musca domestica, calculated 1.00:1.08, observed 

 1.00:1.07; Anasa tristis, calculated 1.00:1.11, ob- 

 served 1.00 : 1.09. Complete data were given in 

 the February, 1915, number of the Journal of Ex- 

 perimental Zoology. 



Sex Controlled by Food Conditions in Bydatina 



Senta: David D. Whitney. 



The cause of the erratic proportion of the two 

 sexes in Hydatina senta has been found to be due 

 to diet. When three pedigreed parthenogenetic 

 races of these rotifers were reared in the labora- 

 tory on a constant and uniform diet of a colorless 

 flagellate, Polytoma, through 181-288 generations 

 in 14r-22 months they produced 96 per cent, to 100 



