306 PROCEEDINGS OF THE ACADEMY OF [April, 



to basi-chromatin stains, has also changed in shape and apparently 

 in structure. What during the growth stage appeared as a homo- 

 geneous mass shows as prophase advances a clearer plasmosome and a 

 darker chromatin part. In smear preparations, when all the chromo- 

 somes can be seen at one time, it becomes perfectly clear that this 

 idiochromosome forms one of the nineteen chromosomes. Fig. 39 

 shows this to be true even into late prophase. This is a smear prepara- 

 tion in which the plasmosome of the same size as the chromosomes 

 may be recognized as a clearer body with a central chromatin band. 

 In early prophase in both smears and sections, when the spireme 

 is splitting or opening into rays, this body may assume a ring 

 shape (fig. 27), showing a lighter central space around which 

 is arranged the chromatin. Because of its close connection with 

 the plasmosome the idiochromosome always appears larger in these 

 stages than any of the other elements, but with its condensation 

 into a ring or dumbbell-shaped chromosome this size relation is lost, 

 and after its dissociation from the plasmosome I was unable to dis- 

 tinguish it from the other chromosomes. Although this idiochromo- 

 some is first seen in C. promethea after the late post-synapsis when 

 the chromatin has lost its staining property, yet its subsequent history 

 make- it seem more than probable that it was present from the earliest 

 stages: whether the net knots of the spermatogonia bear any relation 

 to this or whether the idiochromosome has been separated from the 

 rest of the chromatin during synizesis must remain conjectural. Its 

 condensed condition during the growth stage and frequent early 

 division while the rest of the chromatin is passing through the usual 

 series of changes before entering upon prophase, as well as its close 

 relationship with the plasmosome, point to the fact that, certainly in 

 structure and possibly in function, this idiochromosome shows pecu- 

 liarities which separate it from the other chromosomes. 



6. Metamorphosis of the Spermatids. — The two spermatids which 

 arise as a result of the second spermatocytic division are elongated 

 cells with a rather small nucleus whose chromatin is in the form of 

 granules. In the telophase of the second maturation division, before 

 the nuclear membrane is complete, the chromosomes are more or less 

 condensed and surrounded by the remains of the spindle fibres of the 

 last spermatocytic division (fig. 54); this spindle fibre material per- 

 sists and is later traced to the nebenkern. The nucleus assumes an 

 eccentric position so that it lies very near the wall of the cyst, and as 

 the nuclear membrane is formed, the chromatin becomes more scattered 

 throughout the nucleus and the material of the spindle fibre, which 



