TESTES OF GUINEA-CHICKEN HYBRIDS 51 



This, it will be seen, is a close approximation to the Mendelian 

 statement of germinal segregation and combination. The quali- 

 fications necessary to bring it more strictly within the pale of Men- 

 delism as then known were made in a brief paper*' early in 1903. 



As previously stated, in many of the seminiferous tubules of 

 the guinea-chicken hybrid synapsis occurred and occasionally 

 some cells progressed to the completion of the second division 

 and the formation of spermatids. But even where synapsis 

 was effected there was more or less of a tendency for the union to 

 be incomplete or partial. This was evidenced by the unusual 

 bipartite appearance of the conjugated chromosomes and in an 

 occasional excess of chromosomes over the number (nine) charac- 

 teristic of the corresponding stage in the chicken or the guinea. 

 In cases of such excess the extra chromosomes had the smaller 

 size of the univalent type. 



Even in normal spermatogenesis one not infrequently encoun- 

 ters fluctuations in the number of chromosomes. This is true 

 to such an extent indeed that, judging from iny own studies on 

 the chromosomes of various birds and man, one is led strongly to 

 the opinion that in these instances at least we are dealing with 

 compound chromosomes which may occasionally resolve them- 

 selves into simpler components and in consequence exist in 

 greater than the typical number when ready for division. On the 

 other hand, instead of an increase there may be a reduction below 

 the recognized haploid number, as I have shown to be true in 

 man where the spermatocytes of the second order typically appear 

 as five (or seven with the accessories) instead of the expected 

 ten (or twelve) ; or in the case of the guinea, the chicken, and the 

 pigeon, four (five with the accessory) instead of eight. 



While in the guinea-chicken hybrids the secondary spermato- 

 cytes tend to exhibit four (or five) chromosomes in division, there 

 is more irregularity than in the normal fowl. If my interpreta- 

 tion that the fusion between guinea and chicken chromosomes 

 in the primary spermatocytes is inhibited in some way because of 

 their inherent dissimilarities be correct, the same fact might 

 account likewise for the occasional increase of numbers in the 



" The germ-cell and the results of Mendel. Cincinnati Lancet-Clinic, May 9, 

 1903. 



JOURNAL OP MORPHOLOGY, VOL. 23, NO. 1 



