36 THE entomologist's record. 



M'Lachlan the pioneer, but his work stands out as the earliest of equal 

 importance. I do not know the precise evolution of the study of the 

 neuration in the lepidoptera, and I do not know that we have any 

 separate monographs of the subject. The whole subject is a develop- 

 ment of the present century, and it is not quite easy to classify such 

 work as that of Spuler and others as being embryological or mor- 

 phological ; Comstock and other American authors have given us 

 valuable data over a wide area, whilst the detailed use of it for classi- 

 fication is most ably displayed by such English masters as Meyrick 

 and Hampson. There is still wanting the close investigation of the 

 development of the various types of neuration in the imagines from 

 the primitive outline that exists in the pupa. There is some reason 

 to believe that Avhen this is done, some forms that are apparently 

 identical will be found not to be so, but to be convergent examples of 

 unrelated descent. 



Improvements in the technique of the laboratory have also led to a 

 great advancement in the extent of our knowledge of embryology and 

 development. Such matters as the segmentation of the embryo, as 

 pointing to the nature of insect ancestors, the true structure of the 

 insect head as consisting of primitive segments, and many others, 

 cannot be dealt with briefly. Perhaps it may be admissible, in view 

 of our vain-gloriousness, which is one of the characteristics of our 

 age, to note how one of our discoveries, that of imaginal discs, and 

 the processes of development which their name may shortly typify, 

 really leads us, as a brief epitome of the subject, precisely to the con- 

 clusions as to the nature of metamorphosis that were arrived at by 

 Swammerdam, yet we go back to Swammerdam,not one, but more than 

 two, centuries. Swammerdam's view was that the butterfly already 

 existed in the caterpillar, even in the youngest caterpillar, though the 

 parts Avere very small, very soft, bathed in fluid, and obscured by 

 parts belonging to the caterpillar. He is short of the words embryonic 

 cells and imaginal discs, but he expresses very fairly the facts. It is 

 very curious to find that he expressly combats the theory that the 

 chrysalis is like an egg within which the butterfly develops, and that 

 the same erroneous idea had some acceptance when Weismann' s researches 

 on diptera puptB first became knoAvn ; the fact being, of course, 

 that the necessary embryonic cells do not have to develop from a 

 germinal vesicle, &c., but are all already distributed in their proper 

 places and differentiated so that each group represents only the organ 

 or organs Avhich will arise from at. One no doubt realises a little 

 difficulty in accepting Swammerdam's view that the young caterpillar 

 had ready all the skins he had to cast, and that getting rid of these 

 disclosed the butterfly, Avhich was all the time growing in preparation 

 for the event. We know, of course, that each skin is really a 

 cutaneous secretion, which does not exist until shortly before it is 

 wanted, but if Ave take the view of some modern authorities that the 

 chitin lost at moults is not merely a secretion, but an excretion, 

 Swammerdam must again score even here very decidedly. What Ave 

 may Avell marvel at is that Swammerdam arrived at his conclusions 

 from some very simple observations. They Avere, hoAvever, carefully 

 made, frequently repeated, looked at on all sides, and Aveighed and 

 pondered with a love of Nature and a genius for understandhig her 

 which can never fail to have their reward. 



