THE SPERMATOGENESIS OF THE SPIDER. I 77 



SIGNIFICANCE OF THE ACCESSORY CHROMOSOME. 



Considerable attention has been paid to the distribution of ac- 

 cessory chromosomes to the spermatids because opinions have 

 differed in regard to it. Nothing could be clearer than the fact 

 that, in the spider, during the first maturation mitosis, the two 

 accessory chromosomes pass bodily over into one of the two 

 daughter cells. In the second maturation mitosis the question 

 is far more difficult to answer, partly because but one half of the 

 cells contain the accessory chromosomes anyhow and partly be- 

 cause the V-shaped chromosomes attached to the equator of the 

 spindle by their apices, cause a branching in the equatorial plate 

 and thus the monaster is a much less clear subject for study than 

 is found in the first spermatocytic monaster. A number of 

 favorable cases were found, however, in which the two accessory 

 chromosomes pass to but one pole and such cases, together with 

 a careful study of the spermatids, have convinced me that not 

 only in the first division, but also in the second the accessory 

 chromosomes pass to but one pole, and are therefore, distributed 

 to only one fourth of the spermatids (PI. I., Fig. 28). In this 

 respect my results differ from all other workers yet heard from. 

 Henking and Paulmier found the hetero-chromosomes dividing 

 in the first spermatocytic division, but passing undivided to one 

 daughter cell in the second ; McClung, Sutton and Blackman 

 hold just the reverse. They find them taking no part in the first 

 but dividing in the second division. In either of the above cases 

 the result would be the same, /. t\, one half of the spermatids 

 would contain no heterochromosomes, while the other half would 

 contain them and could be called what Henking has styled 

 " bevorzugten Tochterzellen." Montgomery finds the hetero- 

 chromosomes dividing like the ordinary chromosomes in both 

 divisions and they are, therefore, present in all of the spermatids, 

 while in the spider they seem to stand aloof in both of the 

 maturation mitoses and are, therefore, distributed to but one 

 fourth of the spermatids. 



In consideration of our limited knowledge in regard to the 

 heterochromosome, and of the fact that nothing is known as to 

 what part this peculiar nuclear element plays in fertilization, it is 

 perhaps premature to say anything in regard to its significance. 



