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linville: pulmonate gasteropods. 223 



the size of the centrosphere itself. The existence of the Latter extreme 

 affords strong reason for believing that the entire centrosphere may be- 

 come stained, for, by a proper serial arrangement of several prepara- 

 tions, one can see that the clear region of the centrosphere surrounding 

 the centrosome is gradually encroached upon by the centrifugal advance 

 of the stainable region, until the entire centrosphere is deeply and 

 homogeneously stained. It is quite possible that the cases of faintly 

 stained centrosomes may be due either to understanding, or, what is 

 more probable, to protracted decolorizing. 



In taking up the detailed description of the maturation spindles, I 

 shall follow the order indicated in the discussion of the same structures 

 in Limax maximus ; that is, I shall begin with the earliest stage in the 

 first maturation spindle. It will be remembered that in Limax maxi- 

 mus the earliest stage obtained was one in which the condition of the 

 chromosomes of the first maturation spindle already indicated the 

 telophase. That was a uterine egg. 



All the eggs of Limnsea elodes were taken after being laid. The 

 earliest stage obtained was that shown in Plate 1, Figure 2.^ The spin- 

 dle is fully formed ; it surrounds the disintegrating germinative vesicle, 

 and already has a radial, though deep, position. At either pole of the 

 spindle is a well-developed aster, at the centre of which appears a mass 

 of minute granules, stained yellowish-brown. In the midst of this mass 

 it is possible with an immersion lens to distinguish a very small and 

 faint centrosphere, containing an extremely small centrosome (not to be 

 seen in the drawing). The inner aster is curiously modified by the 

 sperm aster, a phenomenon to which I shall refer later on. 



A stage in the egg of Limax agrestis, similar to this, is shown in 

 Plate 3, Figure 14. In this case the germinative vesicle, judging from 

 the rather uneven arrangement of the chromosomes, has just disappeared. 

 The spindle here is central, and in this respect differs from the condition 

 shown for Limnaea in Plate 1, Figure 2, where one pole of the spindle is 

 near the centre of the egg. In Figure 14 both the position of the spin- 

 dle and the condition of the spermatozoou indicate a stage younger 

 than that of Limnaea (Figure 2), but the condition of the germinative 

 vesicles indicates that it is older than Limnaea. 



In the eggs of Limnaea I have seen frequently the typical flattening 

 of the animal pole preceding the formation of the first polar cell (Plate 1, 



1 (Plate 4, Figure 25, represents the egg of Limax agrestis before it leaves tlie 

 hermaphrodite gland, and shows the condition of the germinative vesicle at this 

 stage.) 



