DEGENERATE SEXUAL REPRODUCTION. 1 87 



SUMMARY. 



1. Parthenogenesis was formerly believed to be of wider occurrence 

 than it really is, but it is definitely known to be not uncommon in lower 

 animals. 



2. Artificial, pathological, occasional, partial, seasonal, juvenile, and 

 total parthenogenesis must for clearness be distinguished. 



3. The occurrence of parthenogenesis is especially well seen in rotifers, 

 crustaceans, and insects. 



4. It is rare among plants, but certainly occurs in some of the lower 

 forms. 



5. The offspring of parthenogenetic ova is very diverse. 



6. The effects of parthenogenesis on the species deserve consideration, 

 especially by those who find in sexual intermingling the sole fountain of 

 specific variation. 



7. Parthenogenetic ova, so far as observed, form only one polar body. 



8. Parthenogenetic ova are here regarded as imperfectly differentiated 

 female cells, retaining certain male or katabolic characteristics. 



9. In origin parthenogenesis is regarded as a degeneration from the 

 ordinary sexual process. 



10. The voluntary parthenogenesis of bees is taken as a concrete 

 illustration. 



LITERATURE. 



See especially the already cited works of Balfour, Brooks, Hensen, 

 Minot, Rolph, Sachs, Weismann ; also — 

 Owen. — Parthenogenesis; or, The Successive Production of Procreating 



Individuals from a Single Ovum. London, 1849. 

 Von SiEBOLD. — Beitrage zur Parthenogenesis. Leipzig, 1871. 

 Leuckart. — Art "Zeugung" in Wagner's Handworterbuch d. Physiol., 



Bd. IV., 1853. 

 GERSTiECKER. — Bronn's Klassen und Ordnungen des Thierreich, Vol. V., 



Arthropoda. 

 Brooks, W. K. — Law of Heredity. Baltimore, 1883. 

 Simon, F. — Die Sexualifat, &c., Inaug. Dissertation. Breslau, 18S3. 

 Blochmann — Ueber die Richtungskorper bei Insekteneiern. Biolog. Cen- 



tralblatt, VII., and Morpholog. Jahrbuch, XII. 

 Weismann, A. — Beitr. zur Naturgeschichte der Daphnoiden. Leipzig, 



1876-79. Ueber die Zahl der Richtungskorper und liber ihre Be- 



deutung fiir die Vererbung. Jena, 1887. 

 Weismann, A., and Ischikawa, C. — Berichten der naturforsch, Gesell- 



schft., Freiburg, III., 1887. 

 Hudson and Gosse. — The Rotifera. London, 1886. 

 Plate. — Beitrage zur Naturgeschichte der Rotatorien, Jenaische Zeitschft. 



f. Naturwiss, XIX., 1886. 

 Karsten, H. — Parthenogenesis und Generations- Wechsel im Thier und 



Pflanzenreiche. Berlin, 1888. 



