THE VEGETABLE AND ANIMAL KINGDOMS. 117 



life, or of the relations which an organized being bears to 

 the external world." Excepting in the relative situation 

 of the annelida and a few of the mammal orders, the pari- 

 ty is perfect ; nor may even these small discrepancies ap- 

 pear when the order of fossils shall have been further in 

 vestigated, or a more correct scale shall have been form 

 ed. Meanwhile, it is a wonderful evidence in favor of 

 our hypothesis, that a scale formed so arbitrarily should 

 coincide to such a nearness with our present knowledge 

 of the succession of animal forms upon earth, and also 

 that both of these series should harmonize so well with 

 the view given by modern physiologists of the embryotic 

 progress of one of the organs of the highest order of animals 

 The reader has seen physical conditions several times 

 referred to, as to be presumed to have in some way go- 

 verned the progress of the development of the zoological 

 circle. This language may seem vague, and, it may be 

 asked — can any particular physical condition be adduced 

 as likely to have affected development ? To this it may 

 be answered, that air and light are probably amongst the 

 principal agencies of this kind which operated in educing 

 the various forms of being. Light is found to be essen- 

 tial to the development of the individual embryo. When 

 tadpoles were placed in a perforated box, and that box 

 sunk in the Seine, light being the only condition thus ab- 

 stracted, they grew to a great size in their original form, 

 but did not pass through the usual metamorphose which 

 brings them to their mature state as frogs. The proteus, 

 an animal of the frog kind, inhabiting the subterraneous 

 waters of Carniola, and which never acquires perfect 

 lungs so as to become aland animal, is presumed to be an 

 example of arrested development, from the same cause. 

 When, in connexion with these facts, we learn that hu- 

 man mothers living in dark and close cells under ground, 

 that is to say, with an inadequate provision of air and 

 fight — are found to produce an unusual proportion of de- 

 fective children,* we can appreciate the important ef- 

 fects of both these physical conditions in ordinary repro- 

 duction. Now there is nothing to forbid the supposition 

 that the earth has been at different stages of its career 



* Some poor people having taken up their abode in the cells 

 ander the fortifications of Lisle, the proportion of defective infants 

 produced by them became so great, that it was deemed necessary 

 to issue an order commanding these sells to be shut up. 



