Decembee 29, 1922] 



SCIENCE 



759 



and to N — 6.0594 X 10^3, is 2.166 gm/cmS or 

 only a little lower than the lowest value quoted 

 ■by Davey.!* 



The value N = 6.0594 X 10-^ is «iuivalent 

 •to a factor 1.65033 X lO-^* (log-i 24.2175704 

 for converting atomic or anoleeular weights to 

 grains. 



The second method, depending upon the 

 value of /}, requires in addition a determination 

 of the potential aipplied to an X-ray tube. The 

 work of Blake and Duane^^ may be consid- 

 ered as a detea'mination of d in terms of Ji. 

 The values of h collected Iby Birgei^ vary some- 

 what among themselves but 6.560 X 10^^'' 

 seems a reasonable mean value of the results 

 not depending upon X-ray wave-lengthsj and 

 this gives d^ ^„ = 3.0303 X lO-s or 0.058 



^ CaCOs 



per cent, higher than the value given above. 

 This is within the range permitted by the prob- 

 able error in the value of h just taken. 



The following constants are therefore recom- 

 mended to be used until other values are agreed 

 upon; to the accuracy indicated iby the log- 

 arithms. 



Grating space of calcite: 



3.028 X 10-^ cm. (log-l 8.48116) 

 Number of molecules per mol: 



6.0594 X 1023 (log-l 23.78243) 

 Molybdenum K-radiation wave-lengths : 



ai 0.70783 X 10-8 cm. (log-i 9.84993) 

 ao 0.71212 X 10-8 cm. (log-l 9.85255) 

 L. W. McKeehan 

 Eesearci-i Laboratories of the Amer- 

 ican Telephone and Telegraph 

 Company, and the Western Elec- 

 tric Company, Incorporated, 

 September 20, 1922 



PERIPHERAL MIGRATION OF A CENTRIOLE 

 DERIVATIVE IN THE SPERMATO- 

 GENESIS OF (ECANTHUS 

 In 1920 Mr. Chas. S. Driver began at Colum- 

 bia University a studj' of the male germ cells 

 of a common tree-cricket, Qicanthus nigricornis 

 Walker, an Orthopteron insect of the family 



14 Loc. cii.,13 assuming the value attributed to 

 Eetgers is 2.167 and not 1.167 as printed. 



15 F. C. Blake, "W. Duane, Phys. Rev., (2), 10, 

 624-637 (December, 1917). 



ISXoc. cit.l 



Gryllidce. His preliminary study convinced 

 him that, during the changes undergone by the 

 spermatid as it begins to lengthen into the 

 mature sperm, the entire distal centrole mi- 

 grates posteriorly along the axial thread, 

 eventually forming a terminal "plug" for the 

 caudal sheath at its distal extremity. "While a 

 peripheral migration of part of the central ap- 

 paratus in the spermatids of invertebrates was 

 not hitherto entirely unknown, previous ac- 

 counts are few in number and somewhat con- 

 flicting in substance. A reexamination of this 

 phenomenon was, therefore, of considerable 

 interest. The untimely death of Mr. Driver 

 left his work incomplete and his material was 

 delivered to me for further study. Driver de- 

 serves much credit for the excellence of the 

 preparations, which are remarkably well fixed 

 and stained. The method of Benda was used 

 for fixation, and the sections were stained ac- 

 cording to the alizarin-crystal violet technique. 

 My observations were made at a magnification 

 of 1,100 to 1,650 diameters, somewhat higher 

 than that used by Driver in his survey of the 

 material. 



After a careful study I have reached a dif- 

 ferent conclusion in regard to the migrating 

 "centriole" from those of Driver and earlier 

 observers. Although there is in the spermatids 

 of CBcanthus a peripheral migration of a body 

 which appears much lUce a centriole and stains 

 in a similar manner, I am able to demonstrate 

 that the migrating body is not an entire cen- 

 triole, but only a portion or derivative of the 

 distal centriole. 



In early spermatids of QDcanthus the central 

 apparatus appears as a bar which lies per- 

 pendicularly to the nuclear membrane. The 

 axial thread has already appeared at this early 

 stage. The bar constricts in the center, dividing 

 into a proximal and a distal centriole. Almost 

 immediately a small portion of the latter, en- 

 circling the axial thread, is budded off and 

 begins a migration along the thread. As it 

 moves distally it increases rapidly in size, and 

 eventually becomes as large as both proximal 

 and distal centrioles combined. It reaches a 

 permanent position at the distal extremity of 

 the caudal (mitodhondrial) sheath. The re- 

 mainder of the distal centriole continues to lie 



