444 HISTOLOGY 



the typical accessory chromosome (unassociated with micro- or idio- 

 chromosomes) is found only among the Orthoptera, where it has been 

 described by Sutton ('oo-'o2) in Brachystola magna; by de Sinety ('01) 

 in one of the Acridida, and several of the Phasmida; by Eaumgart- 

 ner ('04) in Gryllus domesticus; by Stevens ('05) in Stenopelmatus and 

 Blatella germanica; and by Otte ('06) in Locusta viridissima. Moore 

 and Robinson ('05) claim that in Periplaneta Americana the odd chro- 

 mosome is merely a plasmosome, dissolving before each division and 

 re-forming after it. 



A different terminology has been employed by various writers to 

 designate the accessory chromosome of McClung. Miss Stevens calls 

 it the "odd chromosome"; Montgomery formerly used the term "chro- 

 matin nucleolus"; de Sinety designates it the "chromosome speciale"; 

 and Wilson names it the " heterotropic chromosome," where it appears 

 in the Hemipters. 



Much theory and speculation has arisen in a regard to the accessory 

 chromosome and its supposed connection with the inheritance and de- 

 termination of sex. Castle ('03) has developed a theory of sex in which 

 he applies Mendel's principle of segregation to sex phenomena. He 

 shows that sex production may be explained as the result of a Mendel ian 

 segregation, transmission, and dominance of sexual characters. The 

 theory has recently been more fully elaborated by Wilson ('06) and 

 extended to apply to cases where either of the three forms of hetero- 

 chromosomes (Montgomery) prevail : microchromosomes (small chromo- 

 somes); idiochromosomes (a pair of unequal chromosomes); or 

 a heterotropic chromosome. The common character of heterochro- 

 mosomes is their compact nature and deep staining reaction during the 

 various stages of growth and maturation when the ordinary chromo- 

 somes pass into the nuclear reticulum. The theoretical discussion of 

 the observations on the accessory chromosome and the far-reaching 

 conclusions which may be drawn from the observed facts are better 

 understood after a brief presentation of a concrete example. To this 

 end Aplopus Mayeri (Phasmid), the giant walking-stick insect of 

 Loggerhead Key, Florida, serves the purposes admirably. Here the 

 accessory chromosome can be traced from its first origin in the secondary 

 spermatogonial cells through the entire history of spermatogenesis into 

 the nucleus of a half of the spermatids, where it finally disappears during 

 the time that these undergo metamorphoses into spermatozoa. Except 

 for the number of chromosomes, the facts, as they here obtain, agree in 

 essential points with Wilson's latest report (after an extensive compara- 

 tive study of smear, unfixed, and fixed and stained preparations) for 

 Anas a tristis. 



The primary spermatogonial cells (Fig. 407, i) have a resting nucleus 



