Further Studies on Reproduction in Sagitta. 299 



respect was very striking. In some specimens all of the chromo- 

 somes were in the equatorial plate without exception; in others 

 the polar chromosomes were seen in every spindle ; in still others 

 both conditions were found in the same cyst. This variation was 

 also. found in the aceto-carmine preparations of the three Naples 

 species. The number of chromosomes in all of the species studied 

 is the same, nine for the reduced number. The individual chro- 

 mosomes are much more distinct in aceto-carmine preparations, 

 and I think there can now be no doubt as to the count. 



Figs. 82 and 83 are first spermatocyte equatorial plates of Sag- 

 itta bipunctata from spindles in which all of the chromosomes 

 were in the equatorial plates; Fig. 84 from a spindle where eight 

 were in the equatorial plate and one daughter chromosome (.Ti 

 and X2) at each pole. All of the spindles from this individual 

 showed the polar chromosomes. Some of these spindles also 

 showed the tetrad nature of the chromosomes (Fig. 85). Fig. 86 

 is a prophase showing the premature division of one chromosome 

 (x). Sagitta inflata proved to be the best material for studying 

 the spermatocytes with aceto-carmine. Fig. 87 is an equatorial 

 plate containing the nine chromosomes, and Fig. 88 a side view 

 of a spindle with the two daughter chromosomes (x) near the 

 poles of the spindle and in different positions, so that they appear 

 somewhat unequal in size. In spindles which do not show the 

 prematurely divided chromosome, one often sees a larger bent 

 chromosome (Fig. 89), which apparently is the erratic one, and 

 may or may not divide precociously. It will also be noticed that 

 this chromosome is attached to the spindle fibers in a different 

 way from the others. Fig. 90 shows the polar chromosomes in 

 such a position that they look equal, and in Fig. 91 they are already 

 dividing precociously a second time. Fig. 92 is a second sperm- 

 atocyte spindle showing the polar chromosomes. Fig. I, a to h, 

 shows the various forms which the bivalents may assume in first 

 spermatocyte prophases and metaphases. The dumb-bell form 

 (a) is by far the most common; h I have seen only once; while the 

 other figures are not infrequent in aceto-carmine preparations. 

 Fig. 93 also shows in an oblique view of a daughter plate the split- 

 ting of the chromosomes for the second maturation mitosis. 



