Dr. Burnett on the Development of Viviparous Aphides. 75 
ty of Steenstrup’s doctrine, I would rather present them as broadly 
indicating that, after all, this doctrine in question involves no 
conditions excepting those belonging to a modified form of gem- 
miparity. All the instances of Polyps, Acalephs, Worms, Insects, 
&e., all would then be classed in the same category, and the va- 
nations in manifestation would belong rather to the economical 
relations of the animal, than to any intrinsic difference of physi- 
ological process. ‘Thus the Distoma-nurses instead of being de- 
veloped to a condition resembling at all their parent, remain per- 
sistent on a low form, and not only is their whole zoological 
character undeveloped, but they also experience morphological 
changes tom the developmental process which immediately go 
on within them. All this is in perfect keeping with their econo- 
my, as animals, for the low order of their conditions of life does 
Fh hecessitate a higher and more truly zoological form of these 
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mnaterial for the development of its endogenous germs. 
low erein, then, would appear to consist the prominent morpho- 
ogical differences observed in this category of phenomena, and I 
need not labor further to show that they are irrelevant of the 
primary essential conditions of these curious processes. 
peer se to me to be the highest, both physiological and 
Fs a interpretation that can be advanced for these phenom- 
and to a Steenstrup has so ingeniously collected and collated ; 
hues advance the view that these intermediate individuals or 
PRN are not intrinsically and zoologically the same as their pa- 
uts, but furnish examples of how dissimilar animals may arise 
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aon statement is made erhaps more strongly and exclusively than the present 
f our knowledge would warrant, but I throw it out much in a suggestive ae 
: i i tof.” 
'S no subject in Physiology more interesting comprehensive than th 
brace all cre he j question now is, does it, as an individual process, 
the categories of phenomena treated by Lovén, Steenstrup, de. 
nomena i ical conditions, or 
Phenomena) imply something beyond and dissimilar fom gemmation # 
