312 PROCEEDINGS OF THE ACADEMY OF [April, 



form the bipartite and quadripartite chromosomes of the prophase 

 (figs. 114, 115 and 117), which in io show a far greater variety of form 

 than in any of the other species described. In the very beginning 

 of the prophase, when the chromosomes are forming from the split 

 section of the spireme, the idiochromosome so compact and darkly 

 staining throughout the growth period, may be seen to be composed 

 of two parts, a paler-staining plasmosome and beside and upon this a 

 chromatin mass : later the plasmosome fades and this peculiarly formed 

 chromosome is no longer distinguishable from the others. A sperma- 

 tocyte equatorial plate shows thirty-one chromosomes, and the meta- 

 phase and anaphase of the first maturation shows that this division 

 is equal and reducing (figs. 119 and 120). The second division is also 

 equal and separates whole chromosomes along the longitudinal axis. 



Throughout almost every step the centrosome can be traced as a 

 dark granule surrounded by an archoplasmic mass. As prophase 

 advances, astral rays are seen about the centrosomes, which at this 

 time have divided and appear as dumbbells, and from them astral 

 fibres radiate in all directions, becoming especially well developed 

 on the side toward the nucleus. Of equally marked development are 

 the spindle fibres, which in the telophase of the second division maj be 

 traced directly to the nebenkern of the spermatid, while a clear ves- 

 icle, the idiozome, lying on one side of the nucleus of the spermatid, 

 can also be traced to the archoplasmic mass surrounding the centro- 

 some of former stages. 



The cells, which after the second division are irregularly placed, 

 are now arranged with their nuclei against the wall of the cyst so that 

 the entire wall is covered with the heads of the spermatozoa, while the 

 tails project into the lumen (Pi. XXVI, figs. 13-1 and 132). During the 

 development of the spermatozoon marked changes occur in the nucleus : 

 the chromatin becomes granular and scattered and the nucleus de- 

 creases in size and frequently bends through an angle of 90° to 180°; 

 later, when the condensation of the nucleus becomes more marked and 

 the tail elongates, the cells again change their position, coming to lie 

 with their heads crowded together and their tails parallel (figs. 133, 

 134 and 135). 



Samia cecropia. 



This species was found abundantly on maples and many bushes 

 about Philadelphia. Development is very similar to that of the 

 other forms described. The resting spermatogonia show one or two 

 net knots ; these are more compact than those of other species and,, 

 unlike them, are surrounded by a clear area. Figs. 140-142 show 



