568 EXPEEIMEXT STATION RECOED. 



On the ergot of Equidse, S. Yoschida {Jour. Col. Agr. Tohoku Imp. Univ., 

 6 (1915), No. 8, pp. 171-190, pis. 2). — The author presents evidence tending to 

 show that the callosity and ergot which present Equidse bear are not rudi- 

 mentary pads, as claimed by some, but are rudimentary digits. 



The cost of horse labor, F. R. Taylor (Breeder's Gaz., 68 (1915). So. 15, 

 p. 609 ) . — Data are given showing three years' records of all items, such as feed, 

 labor, pasturage, and incidentals, including shoeing and veterinary services, that 

 go to make up the cost of horse labor. The cost per hour of labor was estimated 

 to be 10.83, 13.05, and 13.67 cts. for the respective three years. 



Causes of sterility in the mule, J. E. "Wodsedalek (Biol. Bui. Mar. Biol. 

 Lab. M'oods Hole, 30 (1916), Xo. 1, pp. 1-56, figs. 52).— This article reports 

 an extensive study made in the zoological laboratories of the University of 

 Idaho. 



The mule partakes of the qualities of both the sire and the dam, but appears 

 to resemble the ass more than the horse both in structure and habits. It 

 was found that the greatest difference seems to lie in the relative number of 

 chromosomes in the cells of these two animals. " The horse has 37 and the 

 mule 51. This suggests that the number in the ass is about 65, thus making 

 a difference of 28 chromosomes between the parents of the hybrid. The semi- 

 niferous tubules of the mule contain a much smaller amount of germ cells 

 than do the tubules of the horse. Some of the tubules of the mule are entirely 

 devoid of sex cells. The sex cells of the mule are larger than those of the 

 horse in the corresponding stages. All of the 51 chromosomes in the sper- 

 matogonia! cells of the mule enter the spindle for division. The mitotic fig- 

 ures are normal and there are no straggling chromosomes. The accessory 

 chromosome of the hybrid, which is undoubtedly maternal in origin, resembles 

 entirely the accessory of the horse, which fact shows that this sex-determining 

 chromosome retains its individuality. The period of synize.sis, which is so 

 obvious in the primary spermatocytes of the horse, is lacking in the mule. 

 The spireme of the horse is also lacking in the mule, but is replaced by a 

 continuous network of chromatin threads, parts of which sometimes resemble 

 the spireme to a certain extent. 



" There is no definite time for the pairing of threads or chromosomes in 

 the hybrid ; the synaptic period begins at the time the chromatin thread.s 

 make their appearance and continues through the prophase. The pairing of 

 chromosomes, or pseudoreduction, is always incomplete and very inconstant. 

 The number of chromosomes in the late prophase of the primary spermatocytes 

 varies from 34 to 49. The greatest majority of counts of chromosomes lie 

 between 40 and 45. The expected number, if retluction was complete, would 

 be 25 besides the unpaired accessory. In the late prophase of the primary 

 spermatocytes the bivalent chromosomes can as a rule be readily distinguished 

 from the univalent ones. The number of chromosomes which the various cells 

 lack in order to make the original total of 51, in terms of univalence, can 

 usually be accounted for by the proportional increase in the pre.sence of 

 bivalents in such cells. Up to the early prophase of the primary spermatocytes 

 there seems to be no necessity for the paternal and maternal chromosomes to 

 cooperate in functioning. Each group seems to go on performing its func- 

 tions normally. The real conflict ensues during the various stages of the 

 primary spermatocyte, and is no doubt octasioned by the necessity for coopera- 

 tion on the part of the paternal and maternal chromosomes in the process of 

 conjugation or pseudoreduction. 



"Abnormalities in mitosis occur invariably in primary spermatocytes that 

 attain the metaphase stage. Giant cells are occasionally seen. The chromatoid 

 body, which is very conspicuous and constant in the horse, is entirely lacking 



