466 
peculiarities are economical and extrinsic, and do 
not touch the intrinsic nature of the processes there- 
in concerned. ‘Viewed in this way, the different 
broods cr colonies of Aphididae cannot be said to 
constitute as many true generations, any more than 
the different branches of a tree can be said to con- 
stitute as many trees ; on the other hand the whole 
suite, from the first to the last, constitute but a 
single true generation. I would insist upon this 
point as illustrative of the distinction to be drawn 
THE INSECTA, 
§ 3855, 
discussion of those many points suggested by these 
studies. One of these, is, the relation of this subject: 
to some of the various doctrines of development, 
which have been advanced in late years, such as 
that of Alternation of Generation, by Steen- 
strup, and that of Parthenogenesis by Owen. FB 
have there attempted to show that the phenomena 
of these doctrines, as advanced by their respective 
advocates, all belong to those of gemmiparity, and 
that therefore Alternation of Generation and Par- 
between sexual and g iparous reproducti 
Morphologically, these two forms of reproduction, 
have, it is true, many points of close resemblance, 
put there is a grand physiological difference, the 
perception of which is deeply connected with our 
highest appreciation of individual animal life. 
A true generation must be regarded as resulting 
only from the conjugation of two opposite sexes, — 
from a sexual process in which the potential repre- 
sentatives (spermatic particle and ovum) of two op- 
posite sexes are united for the elimination of one 
germ. The germ power thus formed may be ex- 
tended by gemmation or fission, but it can be 
formed only by the act of generation, and its play 
of extension by budding or by division must always 
be within a certain cycle, which cycle is récom- 
menced by the new act of the conjugation again of 
the two sexes. In this way the dignity of the 
ovum as the primordium of all true individuality, 
is maintained. 
I have thus treated this subject in some detail, 
not only from its wide bearing in the physiology of 
reproduction, but also from its direct relation to 
many phenomena alluded to in the preceding 
pages. In the memoir from which I have made 
this extract (read before the Amer. Acad. Arts 
and §c., Oct. 11, 1863) I have entered into a full 
thenog' is in their implied sense, are misno~ 
mers in physiology. Another point there treated 
in extenso, is the identity of this mode of repro- 
duction we have just described in the Aphididae, 
with that observed in the so-called hibernating eggs 
of the Entomostraca (see above, § 290) and the like 
phenomena observed in nearly every class of the 
Invertebrata. They are all referable, in my opinion, 
to the conditions of gemmation, modified in each: 
particular case, perhaps, by the economical rela- 
tions of the animal, 
See for some recent writings on this peculiar 
form of reproduction with the Insecta, and which 
contain many interesting physiological remarks, 
Leydig, Die Dotterfurchung nach ihrem Vor- 
kommen in der Thierwelt und nach ihrer Bedeu- 
tung, in the Isis, 1848, Hft. 3; also, Einige Bemer- 
kungen tiber die Entwickelung der Blattlause, in 
Siebold and Kélliker’s Zeitsch. II. 1850, p. 62; 
also Zur Anatomie von Coccus hesperidum, in Ibid, 
1853, V. p. 1; Victor Carus, Zur naheren Kennt- 
niss des Generationswechsels, Leipsig, 1849; and 
Siebold, as referred to in my note under § 348 note 
4. I cannot here discuss the often similar and 
dissimilar views to those of my own above detailed, 
expressed by these different investigators.— Ep. 
