495 



quite different from that which Biitschli describes for Limnaeus. The 

 relation of the female pronucleus to the internal aster is also not the 

 same as is so generally given (e. g. by H er twig for Asteracanthion) , 

 in as much as it very late or never comes to occupy the centre of that 

 radiate structure. 



18) The male pronucleus appears, usually in the vegetative hemi- 

 sphere of the vitellus, as a spheroidal structure, and makes its way 

 toward the female pronucleus, near the animal pole. It exhibits an in- 

 crease in size proportionate to the growth of the female pronucleus, 

 from which it does not differ in any constant manner, save that of 

 position. 



19) The male pronucleus does not normally produce in any part 

 of its course, at least with the employment of acetic or osmic acids, 

 any trace of a radiate arrangement in the surrounding protoplasm. 



20) Abnormal fecundation, by the entrance of a number of sper- 

 matozoa into a single vitellus, has come under observation in one in- 

 stance. 



21) These abnormal male pronuclei induce a stellate arrange- 

 ment in the protoplasm of the vitellus in their vicinity. Six such 

 stellate figures more or less remote from the female pronucleus, and one 

 or two in close proximity to it, were observed in this case. 



22) Both male and female pronucleus (of more than half their ulti- 

 mate size) , often appear Avith their more pointed ends, directed toward 

 the centre of a faint stellate figure (the interal aster of the second 

 archiamphiaster) , which lies intermediate between the two. 



23) The pronuclei come into contact very near the surface at the 

 animal pole of the egg. They attain each the size of nearly l / 2 the dia- 

 meter of the vitellus before uniting, and contain a large number (up- 

 ward of 50) of nearly spherical nucleolar bodies. 



24) The stellate figures of the first cleavage-amphiaster make their 

 appearance before the fusion of the pronuclei; they do not always 

 centre in or near the plane of contact between the pronuclei, but may, 

 one or both, take origin near the surface of only one (which ?) of the 

 pronuclei. One of these stellate figures may appear before any trace of 

 the other can be detected. 



25) The fusion of the pronuclei and the metamorphosis of the 

 resultant primary cleavage-nucleus into a spindle are, in Limax, syn- 

 chronous events. 



26) The central «areas« of the primary cleavage-amphiaster em- 

 brace granular differentiations, and the rays of the same show zones of 

 thickenings concentric with the central areas, before the formation of 

 the nuclear disk (Kernplatte) . 



