194 TSfi entomologist's recohd. 



the genus Lencania (a jDurely Agrotid genvis). Then there is the 

 remarkable brotherhood of Cvsjmlia tridens and ps/, whose larvae, 

 under very similar methods of life, are much alike, and their imagines 

 (with the same habits) scarcely distinguishable. Under such conditions 

 therefore, it is evident that the actual relationship of allied larvai on 

 the one hand, of imagines on the other hand may, among Lepidoptera, 

 be very much obscured. Where, however, their conditions of life are 

 similar, the larva?, although active, will obey more or less perfectly the 

 law of embrj^onic resemblance. 



4. — On embryology as indicatinCx lines of descent. — The student 

 in dealing with this cpiestion hns two great points to keep in mind ; (1) 

 whether the similarities which he sees are phylogenetic, that is, whether 

 they are due to the transitory reappearance of the characters of a 

 bygone epoch in the ancestral history, or (2) whether they are oecological 

 in their origin and due to 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. 



As Darwin says : " We are so much accustomed to see a difference in 

 structure between the embryo and the adult, that we are tempted to look 

 at this difference as in some necessary manner contingent on growth," 

 but it must be agreed that there is no reason, if such were the case, why 

 the whole adult system should not be sketched out in the earliest stage, 

 and development proceed continuoiisly along these lines to perfection 

 instead of the transitory appearance of certain structures wliich raj^idly 

 disappear. That the latter hajjpens, therefore, shows that such a 

 supposition as the above is wrong in princijile, and that the changes 

 have a real phylogenetic significance. 



We must also bear in mind that it is almost imjDossible for the same 

 individual to show all the stages of development in the long line of 

 descent through which it has passed ; one will leave out some (perhaps 

 inany) stages, which may be shown in others. The complete study of 

 embryology 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 complete^, the line 

 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 us with the clue 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. 

 W^e aim at obtaining a " natural system." What is this but an indica- 

 tion of the line of descent of the various sj)ecies we study and their 

 connection with each other ? Can we wonder, therefore, that, in the 

 eyes of most naturalists, the structure of the embryo is of more importance 

 than that of the adult ? Darwin says : — " In two or more gTOups of 

 animals, however much they may differ from each other in structure and 

 habits in their adult condition, if they pass through closely similar em- 

 bryonic 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 



