426 FRANK R. LILLIE 
There has been much discussion during the past year concern- 
ing a cytoplasmic basis of certain aspects of inheritance, and a 
consequent re-investigation of the penetration of the spermato- 
zoon. Following Meves’ study ('11) of the réle of plastochondria 
in the fertilization of Ascaris, in which he concluded that ‘‘the 
plastosomes represent the hereditary substance of the cytoplasm 
as the chromatin does that of the nucleus,’ a number of authors 
investigated the penetration of the spermatozo6n in echinids. 
Dantan (711) asserts that in Paracentrotus lividus and Psam- 
mechinus miliaris, the entire spermatozo6n enters the egg, and he 
concludes that fertilization should be defined as the union of two 
complete gametes which fuse nucleus to nucleus and cytoplasm 
to eytoplasm. Witschi(’11) describes a case in Strongylocentrotus 
in which the tail of the spermatozo6n entered in fertilization, but 
he thinks it probable that in this form the tail is oftener left on 
the membrane. Ries (11) describes a curious shedding of an 
involucre in the penetration of the spermatozo6n in Strongylo- 
centrotus, but he believes that the axial structures of head, middle 
piece and tail enter. His account must, however, be accepted 
with considerable reserve until confirmed. Finally, Meves (11a) 
has studied the relation of the middle piece in the fertiliza- 
tion of Parechinus miliaris, and believes as the result of his obser- 
vations that it probably furnishes plastochondria. He says noth- 
ing about penetration of the tail, so it is fair to assume that it 
does not occur in Parechinus. 
The classical accounts of the penetration of the spermatozo6n 
in sea-urchins, according to which the tail is left on the membrane 
and only head and middle piece enter seem to be on the whole 
confirmed so far as the main principle (i.e., the non-essential 
character of the tail in fertilization) is concerned, since both 
entrance and non-entrance have been observed. The tail cannot 
therefore be regarded as supplying a cytoplasmic basis for inherit- 
ance in sea-urchins. 
I have shown that in Nereis the middle piece of the spermato- 
zoon is likewise left on the membrane, so we cannot look to it as a 
cytoplasmic basis for inheritance in this form as Meves does in the 
sea-urchin. On the other hand it is possible that the fixation 
