CHROMATOID BODY IN PENTATOMA. 393 



and in later stages is found near one pole, presenting an appear- 

 ance remarkably like that of an accessory chromosome (Figs. 

 8-10). For such in fact I at first mistook it, even after the dis- 

 covery that a similar body is often also seen near one pole in 

 the second division (Figs. 22, 23); for I supposed this might be a 

 case like that of Ascaris megalocephala, where, according to 

 Edwards ('10) the X-chromosome may pass undivided to one 

 pole in either the first or the second division. The resemblance 

 is indeed most deceptive; and these division-figures have often 

 been exhibited to other observers as "a remarkably clear demon- 

 stration of an accessory chromosome" without at first arousing 

 the least suspicion of the hoax. 



The body in question is nevertheless neither an accessory nor 

 any other kind of chromosome ; though this did not become wholly 

 certain until after a study of the entire spermatogenesis. It is 

 in fact of protoplasmic origin, first appearing early in the growth- 

 period outside the nucleus, whence it may be followed unin- 

 terruptedly through all the succeeding stages until it is finally 

 cast out of the spermatozoon. Upon dissolution of the nuclear 

 membrane it is left lying near the chromosomes, passes without 

 division into one of the daughter-cells in each of the spermato- 

 cyte-divisions, and thus enters but one fourth of the spermatids. 

 In the latter it persists with little or no change until a very late 

 stage, sooner or later wanders far out into the sperm-tail, and 

 is at last cast off altogether. It therefore takes no visible part 

 in the formation of the spermatozoon. 



I have as yet been able to study the testes of only a single indi- 

 vidual of P. senilis: but since the whole history of the chromatoid 

 body is clearly shown in this material the facts will be described 

 because of the emphasis that they place on certain possible 

 sources of error in the study of the numerical and sexual relations 

 of the chromosomes. One of the testes was fixed in Flemming's 

 fluid (the best fixation), one in Bouin's, and both were at first 

 stained in iron haematoxylin. One of the Flemming slides was 

 also stained in light green: this slide was afterwards extracted 

 and successfully restained with safranin and light green, giving 

 a preparation of great brilliancy. The results given by these 

 four methods of staining are entirely consistent. In all cases 



