252 W. WALDEYER. 
doctrine of bisexualism of cells and the significance of the 
directive corpuscles as extruded equivalents of spermatozoa, we 
must expect that in parthenogenetically developing eggs 
no directive corpuscles would be formed. The parthenogenetic 
ege receives no spermatozoa, since it develops without being 
fertilized, and has therefore clearly no need for extruding its 
male element. As a matter of fact, up to that time, no direc- 
tive corpuscles had been observed in parthenogenetic eggs. 
The doctrine of cell-bisexualism and the interpretation of 
the directive corpuscles as extruded male elements has now 
received the first and I must say very severe blow through 
the recent researches of Weismann and Blochmann. Weismann 
and Ischakawa (203, 204) found that in various parthenogene- 
tically developing Crustacea—e. g. Polyphemus, Oculus, 
Moina paradoxa, Daphnia longispina, and others, 
directive corpuscles are indeed formed; but, as must be re- 
garded as a very remarkable fact, never more than a single 
one, whereas in the rest of the animal kingdom two or three 
of them are present. The observations of Blochmann (‘ Biol. 
Centralbl.,’ 1887, No. 30) are well worthy of attention in this 
respect; they establish that in Aphis the parthenogenetic 
eges extrude only one directive corpuscle, while by those which 
develop after fertilization two are extruded. 
Weismann, to whom we are indebted for a series of very 
excellent and extremely suggestive contributions on general 
biological problems, especially on the formation of varieties, 
on fertilization, and on heredity,' has made no delay in coming 
forward with another explanation of the directive corpuscles 
(‘ Ueber die Zahl der Richtungskorper und tiber ihre Bedeutung 
fiir die Vererbung,’ Jena, 1887). 
In order to be able to reproduce in an easily intel- 
ligible manner Weismann’s most interesting interpretations of 
the directive corpuscles, I must refer briefly to our author’s 
1 “Ueber die Dauer des Lebens,’ Jena, 1882; ‘Ueber die Vererbung,’ 
Jena, 1883; ‘ Ueber Leben und Tod. Line biologische Untersuchung,’ Jena, 
1884; ‘Die Continuitat des Keimplasmas, als Grundlage einer Theorie der 
Vererbung,’ 1885; ‘Die Bedeutung der Sexuellen Fortpflanzung fiir die 
Selectionstheorie,’ 1886, 
