1884^ and the Principles of Reproduction . 
manua.s. rgent Wan ‘ Whi ° h '' S " 0t * existing 
In addition to the size, the shape and the penetrative 
deration! Spe ™ atMoa wi, ‘ h -e to be taken Lto Ins" 
5 - Hybrid fecundation leads in part to regular and in part 
to irregular segmentation. Very frequently there 
occui, in addition to the regular segmentations irre- 
gular ones in larger or smaller numbers. According 
to the most recent observations we find regular sp/ 
mentation in the crossing of very heterogeneous and 
very irregular ones, in case, of nearly related species. 
ometimes there appear in the same watch-°-Iass* 
along with the most abnormal phenomena of see! 
mentation which quickly lead to the destruction of 
ie ova, perfectly normal ones, which even give rise 
0 wable frogs. It is almost impossible to admit that 
among the spermatozoa of the same portion of sperm 
and among the ova from the same ovary, so S 
vanehes of constitution may exist as to explain these 
stnking diversities Some quite new and peculiar 
agency must come into play. F 
In order to find a key to this riddle Prof. Pfliiger investi- 
gates the principles of generation as they appear from the 
researches of Pringshe^, Hertwig, Fol, Selenka, Schndder 
Butschli, Strassburger, Elfving, and others. From all these 
researches it may be deduced, as an established principle 
aat generation depends on the principle of the co-operatmn 
of two specific powers, the sperm-nucleus and the ovum 
nucleus. From the observation of Fol, that sometimes 
several spermatozoa penetrate to one ovum, and that then 
there anses fiom such egg a polygastrula with several inva- 
g nations (and that several individuals may arise from ova 
has S hV C h n f ate i? ’ p fldger concludes that each ovum which 
has hitherto been considered as a unity may give rise to 
seveial individuals, the egg, and homologically the sperm 
atoxoon, also corresponding to a plurality of individuals 
, m P 11 ^ 1 ? 16 of du ahsm in generation is, however, still up- 
held by the view that the many germs ad upon each other 
by twos, whilst the superfluous ones perish. 
Prof. Pfliiger cannot ascribe to morphological relation* 
any pait in geneiation. It is a physiological process dp 
pending on the specific interactions of atoms and molecules' 
and independent of any aggregate condition,— consequently 
not subject to any general morphological law. We shall 
