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SCIENCE 



. [N. S. Vol. XXV. No. 631 



mann's, Bouin's and Gilson's fluids, of both 

 Anasa tristis and A. armigera,, that of the 

 first-named species from Massachusetts, New 

 Jersey, Michigan and Arizona. The reexam- 

 ination not only confirms but fortifies anew at 

 every point my former results. The evidence 

 given by these preparations is, in my judg- 

 ment, completely demonstrative that in An-asa 

 tristis: (1) There is an odd chromosome that 

 is one of the largest three spermatogonial chro- 

 mosomes. (2) The number of chromosomes in 

 the spermatogonia is 21, in the ovarian cells 

 22. (3) The odd or ' accessory ' chromosome 

 divides in the first spermatocyte division, but 

 passes undivided to one pole in the second. 

 Half the spermatozoa thus receive 10 chromo- 

 somes and half 11. 



These facts appear with irreproachable 

 clearness in a great number of cells, and with 

 a uniformity of result that I think precludes 

 the possibility of error. The number, size 

 and grouping of the spermatogonial chromo- 

 somes, and the history of the odd chromosome 

 in the second division, are clearly shown in 

 Dr. Learning's photographs (which will be 

 published hereafter, should it seem desirable) ; 

 and both these and the preparations are at the 

 service of any who may wish to examine the 

 evidence on which my conclusions rest. I 

 may add that an odd chromosome also exists 

 in the following genera of coreids that have 

 not hitherto been reported on (the spermato- 

 gonial numbers in brackets) : Pachylis (15), 

 Euthoctha (21), Narnia (21), Leptoglossus 

 (21), Chelinidea (21), Margus (23), Cato- 

 rintha (25), Leptocoris (13), and in the pyro- 

 chorid genus Largus {L. succinctus, 13, L. 

 cinctus, 11). In Catorintha, as in Protenor, 

 the odd chromosome is the largest of the 

 chromosomes. In MetapodiuSj alone among 

 the coreids thus far examined, a pair of un- 

 equal idioehromosomes appear in place of the 

 odd chromosome. 



What is the explanation of this contradic- 

 tion of results? Is Anasa tristis a kind of 

 cytological Jekyll and Hyde which presents 

 itself in different guise to different observers ? 

 Possibly; for I have found in Metapodius 

 terminalis that certain individuals possess a 

 small unpaired chromosome and an odd sper- 



matogonial number (23), while other indi- 

 viduals, unquestionably of the same species, 

 lack this chromosome and have an even sper- 

 matogonia! number (22). I believe (but am 

 not certain) that a similar relation occurs in 

 Banasa calva. The unpaired chromosome is 

 here of different nature from the usual type 

 (as I shall show hereafter) ; but such cases 

 show that differences of result regarding the 

 number of chromosomes should not too hastily 

 be attributed to error on either side. As re- 

 gards Anasa, I can only state that the same 

 result is uniformly given by many different 

 individuals, from widely different localities 

 (including Woods Hole, where the material 

 of Miss Foot and Miss Strobell was procured) 

 and after all the methods of fixation. The- 

 contradiction is, I think, probably due to the 

 difference of method employed. Miss Foot and 

 Miss Strobell having placed their faith in 

 smear-preparations, while I have relied on sec- 

 tions. Without undertaking any discussion of 

 the relative merits of the two methods, I may 

 say that whatever be the disadvantages of sec- 

 tions for the purposes of photomicrography, 

 really well fixed and stained sections are cer- 

 tainly competent for the demonstration of 

 such points as are here at issue, while they 

 have the advantage of leaving the topograph- 

 ical relations undisturbed. But the certain 

 determination of the number of chromosomes 

 in a given species by means either of smears 

 or of sections, demands a more critical treat- 

 ment than the mere matter of counting (or 

 photographing) the number that may lie in a 

 given field of view or even in many fields. 

 The real task is to determine the relation 

 normal to the species by the elimination of 

 occasional variations (such as certainly occur 

 in some species) and of plus or minus errors^ 

 due to accident; and this again is not merely 

 a matter of frequency of occurrence, but alsO' 

 of evidence given by the nature of the chro- 

 mosome-groups taken in detail and as a whole. 

 As far as sections are concerned, it is almost 

 too elementary to require mention that a 

 minus error may arise from the failure of one 

 or more of the chromosomes to lie within the 

 plane of section. This might be due either 

 to a position that is normally at a different 



