112 METAMORPHOSES OF MAN 



existence shows us that the animal is on the road to a 

 final perfect condition; we see them with increased 

 vital activity before the first transformation, and for 

 some time after it. It is indeed a critical period/ not 

 only for insects in general, but for butterflies in par- 

 ticular, in which the animal is, so to speak, re-cast 

 and constructed upon a very different plan from that 

 which was adopted before. It would be idle to dwell 

 upon this fact ; let the reader turn, instead, to the 

 earlier pages of this work; or, better still, to Herold's 

 and Newport's beautiful illustrations. In glancing 

 even at the changes undergone by the nervous system, 

 and in watching the re-alteration and development of 

 the ganglia from hour to hour, we are reminded of that 

 period in the transformations of the mammalian em- 

 bryo when the most intense and energetic action was 

 taking place. 



The insect whilst in the larval condition has only 

 to increase in size, like the infant to which Reaumur 

 compared it. But even from this point of view it 

 exhibits a decidedly embryogenic character, viz., the 

 rapidity of this growth. In fact, it is the common rule 

 among all viviparous animals that the increase in weight 

 and volume, which at first takes place with rapidity, 

 becomes less marked as the organism approaches its 

 perfect form. The human embryo, which is quite 

 distinct about the third week after impregnation, 

 measures at this time 6*75 millimetres in length, and 

 weighs about 12 centigrammes. About the eighth 

 week, or, in other words, thirty-five days after the 

 above-mentioned period, it is 20 millimetres long, 

 and weighs 216 centigrammes. About the fourth 

 month, when it may almost be called a fetus, it 



