GENERATION OF INSECTS. 439 



human embryo is first apodal and vermiform ; not, however, at any- 

 period an articulated worm. The metamorphoses of the germ-cells 

 in the spherical monadiform ovum have laid down the foundation of 

 the nervous system coeval with the first assumption of a definite 

 animal form ; and, by placing it along the back as a myelon or spinal 

 chord, supported by a gelatinous notochord, have stamped the vermi- 

 form human embryo with the characters of the apodal fish. When 

 the four undivided compressed extremities bud out, the form of the 

 abdominal-finned fish, or of the Enaliosaur, is indicated. The de- 

 velopment of the heart, of the vascular arches, of the generative 

 organs with their cloacal communication with the rectum, typify the 

 oviparous reptile. But these stages are rapidly passed, and the 

 special character acquired. 



Let us suppose that man, or any mammiferous animal, quitted the 

 ovum and the parent in the guise of the fish, passed a certain period 

 in water, retaining the branchial structure, the undivided extremities 

 and the cloaca, and acquired only increase of bulk under that guise ; 

 let us suppose that then such larva, seeking some safe hiding-place, 

 returned to embryonic passivity and unconsciousness, and was rapidly 

 transformed into the perfect state. Under this hypothetical modifi- 

 cation of the course of human development, the changes of form 

 would be plainly recognisable, and in the accessory circumstances, 

 as well as the essentials, the mammalian metamorphoses w^ould re- 

 semble those of the insect. 



If, on the other hand, every insect had been developed like the 

 Diptera pupipara, and the changes from e,gg to larva and from larva 

 to pupa had been hidden in the oviduct of the mother, a long period 

 might have elapsed before the recognition of these metamorphoses, 

 and they could only at length have been discovered by a series of 

 embryotomies, like those that have brought to light the corre- 

 sponding metamorphoses of man and the mammalia generally. 



By a premature exclusion and activity of the embryo, and by 

 alternate periods of growth and development, one small group of 

 vertebrate animals, the anourous Batrachia, do actually manifest the 

 correspondence with the metamorphoses of insects, which I have il- 

 lustrated by an instance of hypothetical possibility in man. Nay, do 

 not the Marsupial mammalia offer an example of the premature ex- 

 clusion? It needed only that the young kangaroo, with its equal and 

 rudimental limbs, should possess, like the tadpole or caterpillar, the 

 power of self-subsistence, and have gone on feeding and growing, 

 whilst the further and final changes of form were reserved for, and 

 concentrated in, a future brief period of torpidity, to render the 

 parallel almost complete. The creeping or swimming larva of the 



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