Mat 17, 1907] 



SCIENCE 



779 



bodies of typical constitution, its matura- 

 tioji processes are in accord with those of 

 most other metazoon eggs. 



The 'Accessory Chromosome' in Anasa 

 tristis: Katharine Foot and B.C. Steo- 

 BELL, New York. 



The authors interpreted the so-called 

 chromosome nucleolus of the resting 

 ^ermatocyte as the homologue of the 

 nucleolus of the egg and not as a chromo- 

 some, as maintained by the cytologists who 

 have previously investigated this form. 

 They interpreted the so-called heterotropic 

 chromosome as a bivalent, representing in 

 value two spermatogonial chromosomes and 

 not one. In a series of forty-nine photo- 

 micrographs they traced it from the early 

 prophase to the telophase of the second 

 division, demonstrating its division both 

 in the first and in the second spindle. 

 Three of the photomicrographs showed 

 spermatogonia in which twenty-two chro- 

 mosomes were demonstrated. 



Secondary Chromosome-couplings in Eem- 

 iptera and their possible Significance: 

 Edmund B. "Wilson, Columbia Uni- 

 versity. 



As secondary chromosome-couplings we 

 may designate unions or associations of the 

 chromosomes that take place independently 

 of synapsis, such as those described by 

 Siaety in Leptynia and by McClung in the 

 Acrididse. In the spermatogenesis of the 

 Hemiptera heteroptera such couplings oc- 

 cur in several genera. In Pachylis gigas 

 the 'accessory' or odd chromosome often 

 couples with one member of one of the 

 bivalents in the first spermatocyte-division 

 and passes with it to one pole, but the 

 process is inconstant and appears to be of 

 a casual character. In Thyamta custator, 

 on the other hand, there is a small un- 

 paired chromosome that is always separate 

 from the others in the first division but 

 in the second is invariably coupled with 



one member of the smallest pair of 

 chromosomes and passes with it undivided 

 to one pole. Metapodius presents a stiU 

 more interesting relation. Here a small 

 unpaired chromosome is present in some 

 individuals, but not in aU, in addition to a 

 pair of typical unequal idiochromosomes. 

 The latter show the usual relation to sex- 

 production, while the unpaired chromo- 

 some may be present in either sex and 

 hence is of different nature from the odd 

 or 'accessory' sex-chromosome. Here too 

 the unpaired chromosome is always sepa- 

 rate from the others in the first division, 

 but in the second it is in about 80 per 

 cent, of the cells coupled with one of the 

 idiochromosomes. In a marked majority 

 of cases the coupling takes place with the 

 small idiochromosome, and the unpaired 

 chromosome passes to the male-producing 

 pole ; but in some cases the coupling is with 

 the large idiochromosome. "We should, 

 therefore, expect to find the unpaired 

 chromosome present in a majority of the 

 male individuals and in a minority of the 

 female ones; and this is borne out by the 

 data as far as they go, though they are 

 somewhat scanty. Of seven males (testes) 

 five possess and two lack this chromosome. 

 Of five females (ovarian cells) but one 

 possesses while five lack this chromosome. 

 The conditions are constant in each in- 

 dividual. 



These facts suggest that if the chromo- 

 somes embody the primary factors of 

 heredity, the coupling of chromosomes may 

 give the physical basis of certain forms of 

 character-couplings. For instance, the 

 coupling of the sex-characters with the 

 somatic species-characters observed in cer- 

 tain forms of Mendelian hybrids in Lepi- 

 doptera may be due to a coupling of the 

 sex-chromosome with one of the other 

 chromosomes, of the same general nature 

 as that observed in Metapodius. The 

 study of the chromosomes in such cases in 



