13Y R. j. TILLYARD. 279 



Meyrick's Law. 



In 1893, Comstock(l) gave the name " Meyrick's Law" to the 

 following statement, which was first enunciated by Meyrick in 

 1884: — "When an organ has wholly disappeared in a genus, 

 other genera which originate as oftshoots from this genus cannot 

 regain the organ, although they might develop a substitute 

 for it." 



Stated in this manner, this law may be accepted, provided it 

 is clearly understood what its limitations are. These mav be 

 stated as follows : — 



(1) It must be capable of proof that the organ in question has 

 ivholly disappeared from the assumed ancestral genus. For in- 

 stance, a concealed rudiment of an organ may reappear, after a 

 more or less lengthy period of suppression during the course of 

 evolution of the group. It will be clear that this fact alone 

 must make the application of the law exceedingly problematical, 

 except in the case of very simple and easily examined structures 

 or organs. 



(2) Great care must be exercised in determining what is to be 

 regarded as a substitute ior an organ, as contrasted with an actual 

 redevelopment of the original organ from a concealed rudiment. 



(3) The converse of the law is not necessarily true; i.e., if a 

 genus B shows the loss of certain organs in comparison with 

 another genus A, we are not entitled to state, without further 

 evidence, that B is descended from A; we may only state that A 

 is more archaic than B in respect of the characters in question. 



How little the importance of the safeguards in the original 

 statement of this law has been regarded may be gathered from 

 Meyrick's own later work. In 1895(3), we find him enunciating 

 three "laws" as his guiding principles in the determination of the 

 Phylogeny of the Lepidoptera. These are stated as follows : — 



"(1) A'o new organ can be produced except as a modification 

 o/ some previously eoiisti'ug sti'ucture." 



" (2) A Jost organ cannot be regained.'^ 



" (3) A rudimentary organ is rarely redeveloped.^' (p. 10). 



Of these. No. 2 is Meyrick's Law restated without its original 

 safeguards. This, taken in conjunction with the other two, 



