222 W. WALDEYER. 
At any rate, all writers, if we except A. Schneider (181), 
now agree, firstly, that the sperm-nucleus (“ pronucleus male” 
of van Beneden) can be traced morphologically to the head, 
1. e. the nuclear constituent of the spermatozoon. EE. van 
Beneden has shown this in the most convincing manner in 
Ascaris megalocephala, and has figured the process of the 
entrance in great detail. Secondly, it is agreed (Hertwig, 
Fol, Flemming, Selenka, Platner, E. van Beneden) that in the 
lower animals a single spermatozoon suflices for fertilization, 
that indeed the entrance of more hinders or disturbs the normal 
development (‘‘ Polyspermy ” of O. Hertwig). 
The new experimental studies of O. and R. Hertwig (96) are especially 
interesting in this respect. Abnormal impregnation, followed by anomalous 
developmental phenomena, occurs in hybridization and in polyspermy. So far 
as hybridization is concerned, the brothers Hertwig found that the spermatozoa 
are not dainty (‘‘ walilerisch ”), as they express it, but have a tendency to enter 
any egg of any other species of animal. Since they do not succeed in this, as 
is the case in most attempts at experimental hybridization, the Hertwigs believe 
that the hindrance must lie in the egg. I think that too much stress is here 
laid on the egg-cell by these authors. In my opinion, the difference in form 
and size of the spermatozoa must be taken into consideration, as His (98) 
and C. K. Hoffmann (99) have already remarked. The diversity of form and 
f, Anat. u. Entw. Gesch.,’ i, 1876), E. van Beneden (‘ Bull.,’ loc. cit., 1875), 
for Mammals; Newport (‘ Phil. Trans.,’ 144, 1854), for the Frog; Calberla 
(‘ Zeit. f. wiss. Zool.,’ xxx, 1877), for Petromyzon; Nelson (Phil. Trans.,’ 
1852), Meissner (‘ Zeit. f. nat. Med.,’ 1853; and ‘ Zeit. f. wiss. Zool.,’ vi, 
1855), Leuckart (‘Die menschlichen Parasiten,’ chap. ‘‘ Nematoden’”’), and 
A. Schneider (‘ Monog. der Nematoden,’ 1866), for Nematodes—not forgetting 
M. Barry’s (‘Phil. Trans.,’ 1843) very first discovery of the spermatozoon 
inside the yolk-membrane of the rabbit; yet neither Barry nor, a little later, 
Keber (‘ Untersuchungen iiber die Porositat der Korper,’ Konigsberg, 1854) 
and Bischoff (‘ Bestatigung des von Dr. Newport bei den Batrachien und 
Dr. Bary bei den Kaninchen behaupteten Hindringen der Spermatozoiden in 
das Hi,’ Giessen, 1854), saw the act of entrance ; nor were those observers, 
who were prior to Fol, successful in clearing up the fate of the penetrating 
spermatozoon, or in proving the morphological continuity of Hertwig’s sperm- 
nucleus with the head, i.e. the nuclear element, of the spermatozoon. To 
Fol also belongs, as may be incidentally mentioned, the discovery of the 
“cone d’attraction,” as he called it (“ Empfangnisshiigel”’ of O. Hertwig), 
i.e. a small conical process which the egg-protoplasm stretches up to the 
entering zoosperm. 
