FROM EMBRYOLOGICAL DATA. 13 



respective families, than those which raise them upwards. We may, therefore, learn 

 from this fact, that the diurnal Lepidoptera rank higher than the crepuscular and 

 nocturnal ones. This hint would, of itself, be an ample reward for the time spent 

 in these investigations, even if we did not further learn from them that there is a 

 strict homology between the wings of butterflies and the respiratory vesicles of 

 Annellides, and that the physico-philosophers (I mean particularly the acute Oken) 

 are fully sustained by material facts when they assert that insect-wings are trans- 

 formed gills. 



When the metamorphosis of the larva is allowed to go on undisturbed, this im- 

 mature butterfly, with a comparatively long abdomen, still further contracts. The 

 abdomen especially is considerably shortened (Figs. 17, 18, 19, 19 a) and thick- 

 ened, though its joints remain movable. But the head and thorax and all their 

 appendages are soldered together, and form a solid, immovable case ; and the 

 connection of the external appendages becomes so intimate, that, instead of 

 appearing like independent parts, they assume rather the appearance of outlines 

 of those organs carved upon a surface, as if they were mere indications of the 

 parts to be developed in these regions (Figs. 20, 21, 22), but seeming to be as 

 yet unformed. Nevertheless, as I have shown above, they were all independent 

 shortly before, and have become gradually more and more united in the perfect 

 pupa. 



This transformation is, again, of very great importance with reference to our clas- 

 sification of articulated animals, as it shows that the condition of those Articulata in 

 which head and thorax are united is a lower degree of development than the con- 

 dition of those in which head and thorax are distinct. We have, indeed, here an 

 additional evidence of the views which I have maintained on another occasion, that 

 the Crustacea in which the thoracic and cephalic joints are either entirely inde- 

 pendent of each other, as in the larvae of Lepidoptera, or united in one continuous 

 case, the cephalo-thorax rank below the true Insects, and also that Arachnidse, 

 the spiders, are inferior to the Insects proper. 



The transformation of the pupa into the perfect insect (Fig. 23) takes place in 

 the same manner as the transformation of the larva into a pupa, in consequence of 

 another moulting, during which the surface of the animal undergoes its last changes, 

 and assumes the characteristic peculiarities of the perfect insect. The difference, 

 however, between the perfect Lepidopteron and the pupa is much less than the 



transformation is also taking place in the anterior feet of the caterpillar, for the larger legs of the but- 

 terfly begin to form. But, as a similar transformation is going on in the oral organs, the caterpillar loses 

 its desire to eat and power of mastication, it ceases to receive food, and prepares itself for its last moult- 

 ing, namely, for its change into the pupa. It seeks for this purpose an appropriate place, where it can 

 lie, hang, spin, or attach itself, and it accomplishes this, its last business, the same as its earlier ones, with 

 great care and consideration. After its situation and web are prepared, it reposes a few days, then strips 

 off its skin, and now presents itself as a pupa, with the visible limits of a butterfly." 



It is surprising that this observation should not have led its able author to trace these facts further, and 

 to recognize their bearing upon the classification of Articulata in general, and that of Insects in particular, 

 as well as upon the appreciation of the relative value of the organs in the various development they pre- 

 sent in this type of animals. 



