SOME PROBLEMS OF REPRODUCTION. 5 
on to a consideration of the causes of the individual repro- 
ductive incapacity of most gametes; of the senescence of the 
individuals produced in the later generations of a long cycle of 
fissiparous reproduction ; and conversely of the rejuvenescence 
induced by karyogamy and other processes, which are classified 
and discussed. A special section is devoted to those modes of 
rejuvenescence which have been confounded under the name 
of ‘‘ parthenogenesis,” but which we may term “ paragenetic ;” 
and a general summary of conclusions closes the present 
study. To keep the exposition clear and continuous I have 
abstained as far as possible from controversy. 
I wish to express my thanks to Professors Mark, Guignard, 
Strasbiirger, and Weismann for their communication of 
reprints of valuable papers not otherwise readily accessible 
to me. 
I have not deemed it necessary to give references for facts to 
be found in every text-book, though I have verified as far as 
possible every statement from the original authorities. In all 
other cases I have cited my authority in a foot-note. 
The following is a list of the text-books and papers of general 
interest to which I may refer the reader. 
Booxs— 
‘Essays upon Heredity and Kindred Problems, 
Trans.), 1889. 
‘ Kvolution of Sex,’ Geddes and Thomson, 1890, 
‘Studien tiber Protoplasmamechanik,’ Berthold, 1886. 
‘Handbuch der Botanik,’ Schenk (in progress). 
‘Pflanzenfamilien,’ Engler and Prantl (in progress). 
‘ Fungi, Mycetozoa, and Bacteria,’ De Bary (Engl. Trans.), 1887. 
‘ Physiology of Plants,’ Vines, 1886. 
‘ Befruchtung und Zelltheilung,’ Strasbiirger. 
‘Neuere Untersuchungen,’ Strasbiirger, 1884. 
‘Protozoa’ (in Bronn’s ‘ Thierreich’), Bitschli. 
‘Comparative Embryology,’ Balfour, 1880. 
‘Introduction to the Study of Embryology,’ Haddon, 1887. 
‘Traité d’Embryologie’ (Hd. Fr.), O. Hertwig, 1891. 
‘Forms of Animal Life,’ Rolleston and Hatchett Jackson, 1888. 
5) 
Weismann (Engl. 
