INSECTA. 249 



so must man through those of the Vertebrate, subkingdom. The 

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

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

 the spherical (hydatid-like) ovum have laid down the foundation of 

 the nervous sj^stem coeval with the first assumption of a definite 

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

 chord, have stamped the vermiform human embryo with the charac- 

 ters of the apodal fish. When the four undivided compressed extremi- 

 ties bud out, the form of the abdominal-finned fish, or of the Enaliosaur, 

 is indicated. The development 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 

 modification of the course of human development, the changes of 

 form would be plainly recognisable, and in the accessory circum- 

 stances, as well as the essentials,, the mammalian metamorphoses 

 would resemble those of the insect. 



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

 Diptera pupipara^ and the changes from egg 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 embryo- 

 tomies, like those that have brought to light the corresponding 

 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 

 illustrated by an instance of hypothetical possibility in man. Nay, 

 do not the Marsupial mammalia offer an example of the premature 

 exclusion ? 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, to render the parallel almost 

 complete. The creeping or swimming larva of the Mammal M'ould 



