BY R. J. TILLY A RD. 225 



In North America, the study of all possible ontogenetic stages 

 of Hetaerina and Archilestes would be of great value. 

 B. The Problem of the Anal Vein. 



In my previous paper {loc. cit.), I showed that the anal vein 

 of imaginal Odonata was secondarily developed by a backward 

 growth from Ac, and I named it the " secondary anal vein," A'. 

 Dr. Calvert {in lift.) objects to the term "secondary," and 

 suggests "recurrent" as a better term. I am quite willing to 

 accept his suggestion, though I fail to see the objection to the 

 term "secondary." A glance at Fig.6 shows how this vein can 

 be actually seen developing backwards in Diphlebia, during 

 larval cuticularisation. In any case, A' remains as the notation 

 for this vein. 



As regards the "anal bridge," Ab, Mr. Herbert Campion tells 

 me that Dr. Ris has already employed (apart from tracheational 

 studies) the notation A* for this vein. Dr. Ris's notation should 

 take priority over mine, but for the fact that the use of the 

 asterisk in notation is an innovation much to be deplored, and, 

 as a matter of fact, " preoccupied " by the general consent and 

 use of centuries. A"* in any printed work (including scientific 

 publications) means "A (see reference below)." To illustrate the 

 impossibility of accepting such a notation, I need only remark 

 that the next author who wanted to use it, and at the same time 

 to refer the reader to the place where Dr. Ris originated it, 

 would have to print the absurdity A** (unless he were lucky 

 enough to get A*t!). Surely such signs as *, f, ||, need not be 

 dragged into our notation at all. They should all be considered 

 preoccupied, by general consent. Concerning the structure of 

 Ab in the Calopterygidce, we see (Figs. 2, 3B, 4) that it really is 

 formed along A^ in the older forms, as I previously stated. In 

 Anisoptera, Aj reaches Cug; in Calopterygidce, it just fails to do 

 so; in Agrionidce and Lestidce, only a remnant of A^ is left. We 

 may, therefore, fairly retain Ab as a unit in the Zygoptera, and 

 define it as " the vein which runs from the posterior end of Ac 

 up to Cug." 



There remains the curious formation Ac' in CalopteryxiFig.SB). 

 This seems to be introduced simply because, in the larva, Ac lies 



