EMBRYOLOGY OF A LEPIDOPTEROUS INSECT. 17 



It is well known that all animals during their embryonic life 

 undergo a series of remarkable changes, both in form and structure. 

 The earliest embryonic appearance of widely different animals is such 

 that it is difficult to say even to what class the embryo belongs, but 

 as development proceeds, the characteristic features of the class are 

 developed. When we come to consider the embryonic conditions of 

 genera and species we find that the similarity of their early stages is 

 much more pronounced, the likeness extending even to small matters 

 of detail. 



It is possible to limit the study of the embryology of insects to the 

 changes that take place within the egg, but it is well known that the 

 larvae and pupae of lepidoptera are essentially embryonic conditions, 

 leading up to the production of the imagines. At the same time, 

 their independent life, their competition in the struggle for existence, 

 and the different conditions of their environment, have led to the 

 formation of habits, and given rise to peculiar characters, which more 

 or less obliterate, as it were, their true embryonic characters. It is 

 necessary, therefore, in dealing with these stages (larval and pupal) to 

 bear in mind two points : — (1) Whether the similarities which one 

 sees are phylogenetic, that is, whether they are due to the transitory 

 re-appearance of the characters of a bygone epoch in the ancestral 

 history, or, (2) Whether they are oacological in their origin, and due 

 to a similar relationship of the animals to their organic and inorganic 

 environment. The characters manifested in the egg-state must almost 

 of necessity belong to the first division ; those in the active larval 

 (considered as an embryonic) condition may belong to the first or 

 second. 



It will be seen, then, that such phylogenetic conditions as the 

 embryological stages of insects offer, indicate the lines of descent 

 through which the species have passed. The complete study of em- 

 bryology must, in time, give us much more correct notions of actual 

 relationships than any other line of enquiry ; for it is highly probable 

 that the embryonic stages show us, more or less completely, the lines 

 through which the ancestral form has been developed, to produce the 

 present condition of its offspring. It is to embryology, therefore, that 

 we must look to furnish the clues to the true relationships which exist 

 between animals, and a true genealogical classification can only be 

 formulated by the aid of the knowledge which it contributes. We 

 aim at obtaining a " natural " system of classification of insects, i.e., 

 an indication of the line of descent of the various species we study, and 

 their connection with each other, and, hence, for this purpose, the 

 structure of the embryo is often of more importance than that of the 

 adult. Darwin says : — " In two or more groups of animals, however 

 much they may differ from each other in structure and habits in their 

 adult condition, if they pass through closely similar embryonic stages, 

 we may feel assured that all are descended from one parent form, and 

 are, therefore, closely related. Thus, community in embryonic 

 structure reveals community of descent ; but dissimilarity in embryonic 

 development does not prove discommunity of descent, for, in one of 

 two groups, the developmental stages may have been suppressed, or 

 may have been so greatly modified through adaptation to new habits of 

 life, as to be no longer recognisable. Even in groups in which the 

 adults have been modified to an extreme degree, community of origin is 



B 



