No. 3.] THE CELL-LIN'EAGE OF NEREIS. 375 



process. Unfortunately the preparations cannot be kept perma- 

 nently. Fairly good permanent preparations may be made by 

 mounting (in balsam or glycerine) specimens hardened in Flem- 

 ming's or Perenyi's fluid and stained with haematoxylin or alum 

 cochineal ; but they are not to be compared with the others. 

 Specimens preserved in Perenyi's fluid are apt to darken in 

 time, possibly through the action of the tannin dissolved by 

 the alcohol when cork stoppers are used. Such specimens often 

 make very good preparations when mounted in balsam without 

 staining. 



I. The Unsegmented Egg, 



The eggs are discharged separately into the water and soon 

 sink to the bottom, where they lie with the animal pole turned 

 downward. Each Qgg is surrounded by a transparent, thick, 

 gelatinous envelope, which causes the eggs, when in masses, to 

 be separated by considerable spaces. Occasionally the enve- 

 lopes of a number of eggs adhere closely together, so that the 

 eggs appear as if imbedded in a common jelly, as is regularly 

 the case with N. cultrifera, and some other species ; this, how- 

 ever, is exceptional, and, as a rule, the eggs move freely amongst 

 one another. To the periphery of the gelatinous envelope the 

 spermatozoa adhere in great numbers, so that the eggs appear 

 to be surrounded by a kind of halo, which, if the water is not 

 changed, soon becomes so dense as to obscure the vitellus 

 within it. 



The vitellus is transparent, finely granular, and contains (in 

 N. limbatd) at least three kinds of elements besides the proto- 

 plasm. These are (i) large oil-drops, (2) small oil-drops, and 

 (3) deutoplasm-spheres. The latter are not present in the eggs 

 of N. megalops, or, if present, are invisible, owing to their 

 transparency. The large oil-drops, which vary in number from 

 ten or twelve to twenty or more, and also vary greatly in 

 size, are arranged in an irregular circle (Figs, i, 2) near the 

 periphery of the vitellus in the lower (vegetative) half of the 

 &gg, which is thereby caused to lie with this pole turned up- 

 wards. If the tg% be turned over, it soon rotates back into its 

 original position, so that it is difficult to follow continuously the 

 history of the upper hemisphere in the living &gg. The small 

 oil-drops (Fig. i) are very minute, highly refractive spheres 



