linville: pulmonate gasteropods. 229 



to find evidence concerning a reduction division in the second matura- 

 tion spindle seemed to me very remote. The number of chromosomes 

 in the first maturation spindle of Limax maximus varies from sixteen to 

 twenty, and sometimes twenty-one or twenty-two of them may be seen. 

 Platner ('86) and Garnault ('88) found for Arion sixteen to twenty 

 chromosomes; but it is quite possible, as Boveri ('90) suggests, that the 

 normal number is really sixteen, — a number which seems to be typical 

 for gasteropods. The fact that in Limax maximus the chromosomes 

 exhibit such variation in size and form, leads me to believe that in the 

 telophase of the first maturation spindle of this species, and possibly cf 

 Arion also, not all the bodies seen are simple chromosomes, but rather 

 that some of them are the result of an appreciable separation of the 

 elements composing the " dyads," so that, while some of the supposed 

 chromosomes are unseparated dyads, others are simply one of the com- 

 ponents of a dyad. I believe the tetrad formation of the chromosomes 

 to be characteristic of the prophase of the first maturation spindle. 

 When the elements of the dyads are very close together, the resulting 

 appearance is that of a very large chromosome, much larger than the 

 smaller ones. The smaller chromosomes occur most frequently near 

 together, either in pairs or suggesting a paired arrangement. That they 

 are actually joined together, I could not demonstrate satisfactorily. 

 There are cases, however, in which it is a matter of considerable doubt 

 whether a mass of chromatin is a single body with a constriction at the 

 middle, dumb-bell fashion, or whether there are really two chromosomes 

 very near together. In one case I was able to make out the sixteen 

 dyads very distinctly in the polar cell (Plate 3, Figure 17), but the 

 chromosomes remaining in the egg were so closely massed that it was 

 impossible to count them. A curious condition is to be noticed in 

 Figure 21. The number of dyads in the polar cell is fourteen, and 

 the number of chromosomes remaining in the egg is also fourteen. 

 This is quite an unusual variation, and it is probable that two 

 chromosomes at either end of the spindle were obscured in some 

 way. The evidence afforded by a single instance, even though as satis- 

 factory as that shown in Figure 17, is alone not sufficient to carry con- 

 viction, but taken with the results I have obtained from my study of 

 Limnaea, affords reasonable ground for belie'ving that the explanation 

 which I have offered of the appearance of chromosomes in excess of 

 the number sixteen is the correct one. 



The eggs of Limnsea are more favorable for following the phases of 

 the maturation divisions. Material fixed in 3 per cent nitric acid showed 



