ACCESSORY CHROMOSOME IN A FROG. 77 



matin matter a solid, somewhat irregular crescentic mass. 

 This mass soon rounds off its angularities and arranges itself 

 along the equatorial region of the cell. The outlines of the 

 individual chromosomes are, for the most part, obliterated at 

 this stage. No further reduction of chromosomes occurs at this 

 division. The dumb-bell-shaped X-body is not difficult to iden- 

 tify in the second spermatocyte at the metaphase. Its identifica- 

 tion is rendered easy by its large size and peculiar dumb-bell 

 shape. (See Figs. 27-28.) Part of the dumb-bell usually is 

 seen projecting above the metaphase plate. This is well shown 

 in Figs. 27-28. 



All attempts to determine the chromosomal number in second- 

 ary spermatocytes in my bisexual specimen proved futile, 

 owing to the haem-alum stain. The dumb-bell X-body divides 

 along with the rest of the second spermatocyte chromosomes. 

 No attempt was made to trace the further history of the acces- 

 sory body in the spermatids and spermatozoa. I hope to take 

 up this matter in another paper. 



THE CHROMATOID BODY. 



A number of investigators of amphibian spermatogenesis have 

 observed and reported the presence of an oval, homogeneous 

 chromatoid body in the cytoplasm of the germ cells. 



King, '07, reported it in Bnfo, and claims it forms the acrosome 

 of the spermatozoon. Herman has found a similar body in the 

 spermatids of Salamandra. Recently Bachhuber reported the 

 presence of such a body in the spermatocytes of the rabbit. It 

 has also been reported for other animals. 



In Rana pipiens the chromatoid body is readily found in the 

 cytoplasm of the secondary spermatogonia. I have never ob- 

 served it in the primordial germ cells of very young larvae. 

 This structure is of fairly large size, oval in shape and stains 

 readily. It bears considerable resemblance to an extruded nu- 

 cleolus, though probably has an extra-nuclear origin. The posi- 

 tion of the body in the cytoplasm varies considerably. In some 

 cells it adheres closely to the nuclear wall; in other cells it is 

 found near the periphery of the cell. During spermatogonial 

 division it does not appear to divide, though it occurs among the 



