372 



SCIENCE 



[Vol. LVI, No. 1448 



ce£e have, as a rule, been more easily accom- 

 plished than the eross-inoeulations between 

 members of the SolanaeeiB and members of the 

 Cueurbitaceae. Sueeessful cross-infections be- 

 tween members of different families are more 

 easily obtained with plants growing under very 

 favorable conditions than with plants growing 

 under unfavorable conditions. 



0. H. Elmer 

 I'owA Agricultiteal Experiment Station 



SPERMATOGENESIS OF THE GARTER 



SNAKE 

 Up to the present no ■work has been pub- 

 lished on the spermatogenesis of the snakes. 

 The only Reptilia which have been studied in 

 any detail have been the lizards, and the recent 

 work of Dalcq and Painter 'has definitely 

 pointed out that an accessory element exists in 

 this group. The work on the spermatogenesis 

 of this species of snake {Thamnophis hutleri) 

 has progressed far enough to make it advisable 

 to publish a few of the details, although the 

 work has not yet been completed. 



The species on which this study is being 

 made was collected in the vicinity of Ann 

 Arbor, Michigan, and was identified by Drs. 

 A. G. Euthven and F. K. Blanchard. It has 

 one of the narrowest ranges of any of the 

 garter snakes but is abundant in that locality. 

 The material has been fixed in Flemming's 

 strong and Flemming's strong plus .5 per cent, 

 urea at both room temperature and cold, and 

 in Allen's modification of Bouin. The best 

 results have been obtained with cold Flemming 

 plus urea, fixed for twenty-four hours, sec- 

 tioned at six micra and stained with Heiden- 

 hain's Iron Hsemx. by the short method of Lee. 

 The material shows thirty-seven chromo- 

 somes in the spermatogonial equatorial plates 

 in the best counts and this is what would be 

 expected from a study of the spermatocyte 

 divisions. There is a border of large bent ixsd 

 shaped chromosomes and an inner group of 

 short rods and round chromosomes. 



In the late prophase and side views of the 

 equatorial plate of the fiz'st spermatocytes the 

 accessory elements form a tripartite body. 

 Polar views of the first spermatocyte show 

 seventeen autosomes and either one or two ac- 

 cessory chromosomes depending on the way the 



plate is turned. At the first division, the tri- 

 partite body divides, two parts going to one 

 pole and one to the other, the double part re- 

 maining more or less fused. A polar view of 

 the first spermatocyte shows five quite large 

 bivalents, two of which are slightly smaller 

 than the other three, eleven medium sized and 

 two microsomes, making eighteen as the hap- 

 loid number. If the double accessory happens 

 to be turned toward the observer, one of the 

 three large ones gives the double appearance. 

 There is little indication of an earlier division 

 of the accessoi-y elements though at tiines the 

 double one may be seen lying closer to the 

 centrosome, indicating ' that it has divided 

 earlier. The first division is the differential 

 division, the two daughter cells receiving the 

 following : one, seventeen autosomes and the 

 double accessory, and the other, seventeen auto- 

 somes and the single accessory. 



The second spermatocyte division then be- 

 comes an equational one so far as the accessory 

 chromosomes are concerned and give rise to two 

 classes of spermatozoa. 



Oogonial counts have not yet been made to 

 determine whether the single or the double is 

 the X ehromos&me, but it might be expected, 

 in light of whart; has been found in the lizards 

 by Painter, that the double one is the X and 

 the single the Y and that oogonial counts 

 should yield thirty-eight chi'omosomes. It 

 would seem in this species of snake, at least, 

 that the accessory chromosomes are found as 

 three separate ones in the speimatogonia, 

 which bears out what Painter has already de- 

 scribed for the lizards. 



Examination of some slides of snake testis 

 of an unknown species has revealed a condition 

 of the chromosomes more like the lizards as 

 described by Painter. This material shows 

 in tlie first spermatocyte division equatorial 

 plates with approximately nine very large and 

 eleven very small chromosomes as the haploid 

 number. Before the complete results are pub- 

 lished, a comparative study of other genera 

 and families will be made in order to deter- 

 mine whether the behavior of the accessory 

 chromosomes in snakes falls in line with what 

 Painter has already described for lizards. 



Llotd E. Thatcher 

 University or Michigan 



