178 



SCIENCE 



[N. S. Vol. XLIII. No. 1101 



homosexual female, 7 cases triplets, a ratio of twins 

 of approximately 1:4:2 instead of the 1:2:1 

 expected if there were no disturbing element en- 

 tering in. The expectation may be brought more 

 nearly into harmony with the facts if it is assumed 

 that in addition to ordinary fraternal (dizygotic) 

 twins there are numbers of "identical" (mono- 

 zygotic) twins of both sexes, and that while in 

 the case of females these are both normal, in the 

 ease of a dividing male zygote, to form two indi- 

 viduals, in one of them the sexual organs remain 

 in the undifferentiated stage, so that the animal 

 superficially resembles a female and is ordinarily 

 recorded as such, although it is barren. The rec- 

 ords for monozygotic twins accordingly go to in- 

 crease the homosexual female and the heterosexual 

 classes, while the homosexual male class, in which 

 part of them really belong, does not receive any 

 increment. This brings the expected ratio much 

 nearer the ratio obtained. 



Any female calf twinned with a male is re- 

 ferred to as a free martin. According to the in- 

 terpretation given, some free martins should be 

 fertile, while others are sterile. It was found that 

 both classes exist. 



CYT0L06T 



The Mitochondria in the Germ Cells of the Male 

 of Gryllotalpa iorealis: F. Payne, Indiana Uni- 

 versity. 



The mitochondria are present in the spermato- 

 gonial cells in the form of granules lying at one 

 side of the nucleus and between the nucleus and 

 cell wall. In the early growth-period the granular 

 appearance is replaced by a thread-like arrange- 

 ment. The threads are grouped into a mass and 

 lie in contact or near the nucleus. They remain in 

 this position and condition throughout the growth- 

 period. In the prophase of the first maturation 

 division the threads come out of the mass and as 

 the spindle forms they take up a position outside 

 the spindle, but extending about half-way round 

 it. The threads are almost as long as the spindle. 

 After the chromosomes have reached the ends of 

 the spindle the elongated mitochondrial threads 

 seem to break near the middle, part of them mov- 

 ing along the spindle toward one pole and part 

 toward the other. The threads seem to be ap- 

 proximately halved. In the second division a simi- 

 lar process takes place. Each spermatid, then, re- 

 ceives a mass of mitochondria. In the transforma- 

 tion of this spermatid into a spermatozoon the 

 mitochondria take part in the formation of the 

 tail, but nothing more. 



Pairing of Chromosomes in the Dipt era: Chas. W. 



Metz, Carnegie Institution of Washington. 



(Introduced by C. B. Davenpoet.) 



A study of the chromosomes in about 75 spe- 

 cies of Diptera, ranging from among the lowest to 

 the highest in the order, reveals the following 

 facts : 



First, a paired association of chromosomes is 

 found to exist as a normal condition in all species 

 studied. 



Second, the two members of each pair of chro- 

 mosomes are homologous elements, of respectively 

 maternal and paternal derivation. 



Third, the association of homologous chromo- 

 somes into pairs occurs at a very early stage in 

 ontogeny (before cleavage is completed) and per- 

 sists throughout the larval, pupal and adult life of 

 the fly. 



Fourth, the paired association is found in all 

 diploid cells, somatic as well as germinal. 



Fifth, it apparently persists throughout all 

 stages in the growth and division of each cell, 

 being evident from earliest prophase to latest 

 anaphase. 



Sixth, to account for this side-by-side approxi- 

 mation of homologous chromosomes exhibited by 

 the flies something more than purely mechanical 

 forces must be taken into consideration. 



The data indicates that pairing must depend 

 upon the qualitative nature of the chromosomes. 

 From this, and the fact that paired chromosomes 

 are homologous chromosomes, the evidence is seen 

 strongly to support the hypothesis that homologous 

 chromosomes are qualitatively similar and that 

 non-homologous chromosomes are qualitatively dif- 

 ferent in their make-up, and that therein lies the 

 secret of Mendelian heredity. 



Chromosome Individuality in Fish Eggs: A. Rich- 

 ards, University of Texas. 



The observation of Miss Morris, that the chro- 

 mosomes from the two parents can be recognized in 

 Fundulus eggs fertilized with Ctenoloints sperm is 

 verified. Furthermore, even in the telophases of 

 cleavage mitoses it is possible to recognize clearly 

 the chromosomal vesicles as separate bodies, and 

 in the resting nuclei the parts contributed by the 

 individual chromosome can be distinguished with- 

 out difficulty. Treatment of the eggs or sperm be- 

 fore or after fertilization by X-rays serves to 

 emphasize this distinctness. 



Studies on the Chromosomes of the Common Fowl 

 (illustrated with lantern slides of photomicro- 

 graphs) : M. F. GuYEK, University of Wisconsin. 



