
ee 



KUIPER, STERIELE SOORTSBASTAARDEN. . 299 
All these animals, which were sterile during many years, while most 
ofthem did noteven mate at all, and gaveno results when crossed-back 
with their parents, were examined as to the cause of their Sterility. 
In this paper an account is given, of the morphological results 
only, the cytological data will be communicated within a short time. 
It was found that sterility of hybrids can be brought about in 
different ways. The genitalia of the examined birds showed various 
conditions of development and degeneration. Some of them looked 
quite normal to the naked eye, but appeared to want motile sperma- 
tozoids. At the other extreme, animals were found, absolutely devoid 
of testes resp. of ovarium. Between these extremes several degrees 
of development ‘were found in one and the same cross 
POLL’s opinion as to the relation between Systematic affinity of 
two species and the degree of sexual development of their hybrids, 
proved to be erroneous. 
We failed to find evidence, in support of the view, that the 
interstitial tissue of the testis is responsible for secondary sex 
characters, (so far as the tuft of male Carolina-ducks was to be seen, 
though very little, with the asexual hybrids as well as with the 
male one.) 
LITERATUUR. 
BAUR, E. Bastardierung in Handwörterb. der Naturwisschenschaften Bd. I. 
GOLDSCHMIDT, R. Einführung in die Vererbungswissenschaft, 2e Aufl. 
Guyer, M. Spermatogenesis of Normal and Hybrid Pigeons, Univ. Cincin- 
nati Bull 22 
HAECKER, V. Bastardierung und Geslechtszellenbildung. Zool. Jahrb. 
_ Suppl. VII 1904. 
HAECKER, V. Algemeine Vererbungslehre le. Aufl. 1911. 
Iwanorr, E. Untersuchungen über die Ursachen der Unfruchtbarkeit von 
Zebroiden Biol. Centralbl. XXV. 1905. 
JOHANNSEN, W. Elemente der exakten Erblichteitslehre 2e Aufl. 1913. 
KoosmMan, H. N., Over de beteekenis van het kruisen van individuen, be- 
hoorend tot verschillende Linné’sche soorten, voor het ontstaan onzer 
huisdieren. Ardea 1918. 
Lroyp-Jones, O., Mules that breed. Journal of Heredity Vol. VII ie rl: 
1916, (hieruit geciteerd: Miss BORING, Ewart, STEPHAN en WHITEHEAD. 
POEL, H., Mischlungsstudien. Sitzber. der Ges. Naturf. Sid. Berlin, 1907— 1908. 
TISCHLER, G., Zellstudiën an sterielen Bastardpflanzen. Arch. f. Zellf. ler Bd. 
1908. 
WODSEDALEK, J. E., Causes of Sterility in the Mule. Biol Bulletin XXX. 1916. 
(Ingezonden: 15 Juni 1920). 
