AND MORPHOLOGY OF APHIS. 217 
chiopoda. It is not known to occur in any of the Lamellibranchiata; and among the 
higher Mollusca the nearest approach to it is presented by the animal (whatever it is) 
which gives rise to the * Synapta-schnecken” (high Gasteropods), and by the Hectocoty- 
ligenous Cephalopoda. 
After this simple statement of well-known facts, I need not remind even the tyro in 
zoology, that there is no evidence of an inverse relation between the occurrence of aga- 
mogenesis and complexity of organization. 
I have hitherto, in the course of this argument, confined myself in the main to the deve- 
lopment of Aphis; but it is only just to observe that the author of the hypothesis brings 
forward yet another original observation in support of his large generalization :— 
* In the freshwater polype, the progeny of the primary impregnated germ-cell retained 
unaltered in that body, may set up, under favourable stimuli of light, heat, and nutriment, 
the same actions as those to which they owed their own origin ; certain of the nucleated cells 
do set up such actions, those, e.g. in the Hydra fusca, which are aggregated near the adhe- 
ring pedicle or foot; and the result of their increase by assimilation and multiplication 
is, to push out the contiguous integument in the form of a bud, which becomes the seat 
of the subsequent processes of growth and development; a clear cavity or centre of assi- 
milation is first formed, which soon opens into the stomach of the parent; but the com- 
munication is afterwards closed, and the young hydra is ultimately cast off from the surface 
of the parent *.”— Lectures,’ 2nd ed. p. 124. 
I have had occasion carefully to watch the process of gemmation not only in Hydra, 
but in many species of all the other subdivisions of the Hydrozoa; and I venture to assert 
that no such process as that described by Prof. Owen takes place in any one of them. 
The bud is from the first in communication with the cavity of the body, of which it is 
å mere diverticulum, whose walls are a little thickened at the extremity. No special cell 
or group of cells can be discovered as the centres whence growth proceeds. No “inte- 
gument” is pushed out by any thing beneath it; but the outer layer of the body of 
the animal thickens and grows pari passu with the growth of the bud. No especial 
accumulation of derivative germ-cells can be seen in any part of the body of any Hydro- 
200» , and before gemmation commences there is no distinguishable difference of texture 
between the part in which gemmation commences and any other portion of the body. 
Furthermore if a complex Hydrozoon, such as a Physophora or Agalma, be examined, it 
will be found that there is no histological distinction whatsoever between that part of the 
body which is to give rise to a free swimming generative zooid, and that which produces 
merely a bract, a tentacle, or a stomach. : 
In this case then, as in that of the Aphis, the hypothesis receives no support from, but 
Is totally opposed by, facts; and I unreservedly adopt the conclusion (long na clearly and 
well expressed by Dr. Carpenter), that * spermatic force ” is but a name without definite 
Meaning, applied to that which is not proven to exist, and the assumption of whose 
existence, even, does not help us a single step towards the understanding of the wonderful 
Phenomena of agamogenesis. 
2 * 99 
* I have cited this passage from the ‘ Lectures’ rather than from the work on “ Parthenogenesis,” as they may 
Supposed to contain the expression of the author’s latest views, 
