328 BULLETIN OF THE 



its protoplasm, especially of the superficial layers. The pigment which 

 is located in the latter follows the depressions of the furrows. 



Of still more interest, since corroborating the observations made on 

 Limax, is the brief statement made (p. 24) concerning the appearance of 

 the spindle and the mutual relation of the conjugating pronuclei in the 

 case of Nephelis. Hertwig has never seen these two structures melt 

 together into a single nucleus, notwithstanding the examination of nu- 

 merous preparations ; not even in cocoons presenting at the same time 

 eggs with conjugated nuclei and others about to undergo the first seg- 

 mentation. He therefore concludes that this fusion stadium can probably 

 be of only short duration. Perhaps the fusion in the majority of cases 

 takes place only when the two flattened nuclei begin to elongate and 

 become metamorphosed into a spindle. 



It seems to me probable that ISTephelis is not unlike Limax in this 

 matter, and that the observer may in Nephelis look in vain for an elon- 

 gation of the pronuclei, since in reality a fusion of these structures is an 

 accomplished fact only when the nuclear spindle is formed. Hert wig's 

 suggestion, that the fusion may take place synchronously with an elon- 

 gation of the pronuclei, does not rest, as I understand, on the observa- 

 tion of an elongated condition, but is inferred to exist from analogy with 

 cases where the two pronuclei fuse and the resultant segmentation 

 nucleus elongates. I would suggest that a still more radical difference 

 may obtain here, and that neither a distinct morphological segmentation 

 nucleus nor an elongation of the separate pronuclei finds expression in 

 the case of Nephelis. 



Brandt's ('77) paper on segmentation in Ascaris aims at a reconcilia- 

 tion of the earlier observations of Biitschli ('73") and Auerbach ('74), by 

 calling especial attention to the amoeboid nature of the germinative vesi- 

 cle, and of nuclei in general. It is possible (p. 374) that the extensive 

 and ramified pseudopodia of the germinative vesicle first segmentation 

 nucleus], which at the time of segmentation are vigorously amoeboid, 

 exercise a strong stimulus upon the contractile yolk substance, and 

 thus favor segmentation. 



The neglect to use reagents explains the fact that Brandt failed to 

 see anything of a spindle structure or its elements, and perhaps also 

 that the radial phenomena which he observed were only such as unfavor- 

 able objects have revealed to other observers. The new nuclear struc- 

 tures which Auerbach describes as vacuoles in the handle of the 

 dumb-bell are only an indication to Brandt, that the nuclear pseudo- 

 podia first to be retracted are those occupying the side of the cell next 



