220 BULLETIN OF THE 



the coarser granular elements of the yolk do not intrude (Fig. 70), but 

 subsequently the force that kept these granulations back seems to yield 

 completely, and no part of the vitellus remains absolutely free from 

 them. 



A condition such as is presented by Fig. 68 might leave one in doubt 

 whether this aster belonged to the male or the female pronucleus. A 

 comparison with numerous other cases (e. g. Fig. 72) leads me to think 

 there is no room to question its being an archiaster, — the remnant of 

 the inner star of the second archiamphiaster. 



When it has attained considerable size, and is consequently in the vicin- 

 ity of the animal pole, the male pronucleus may sometimes be seen in the 

 living egg. In some cases, either from the comparative absence of yolk 

 granules, or from its superficial position, or from both, it may be easily 

 distinguished as a sharply marked spheroidal body (Figs. 21, 30), although 

 nucleoli are not always distinguishable. In fact, both the male and female 

 pronucleus — the latter more superficial, and the former somewhat deeper 

 — were seen and figured in Limax as long ago as 1850 by the Russian 

 naturalist Warneck ('50, Taf. IV. Fig. 10'); although the state of em- 

 bryological science at that time did not allow this very accurate observer 

 to interpret his observations as successfully as may be done to-day. 



The pronuclei ultimately come in contact, and their increase in size 

 does not seem to cease when they touch. They become more or less 

 flattened against each other, but an actual union, as observed in the case 

 of many other animals, is not to be seen here. If it ultimately takes 

 place, as we must conclude it virtually does, the union is so late and so 

 involved in other phenomena as to become entirely unrecognizable as 

 such. It is, therefore, at this point that the egg of Limax presents one 

 of its most interesting and instructive phases. Before proceeding to 

 consider these changes, which belong strictly to the process of segmenta- 

 tion, it is desirable to say a few words concerning some appearances 

 which must doubtless be considered abnormal. Although the observa- 

 tions are meagre, a brief statement of them may be welcome, since, as 

 far as I am aware, no one has recorded similar observations concerning 

 the eggs of Limax, nor indeed of any of the Mollusks. 



For one interested in recent observations upon impregnation the de- 

 scription of the male pronucleus cannot fail to be of interest in a nega- 

 tive way, inasmuch as no allusion has been made to the existence of any 

 special arrangement of the protoplasmic substance immediately surround- 

 ing it. It has been ascertained by several observers, that, in many ani- 

 mals, the male pronucleus early becomes, if not the centre, at least the 



