1889.] 407 



importance of the abdominal characters. Classification and nomen- 

 clature are matters of pure convenience. When, in the dim future, 

 the time may perhaps arrive when every single bird, beast, fish, and 

 insect, every plant, every mineral, existing on earth has been seen and 

 described by somebody or other, then the work of the systematist will 

 be reduced to simplifying as much as possible the congeries of Orders, 

 Families, genera and species. And when, in the still dimmer future, 

 somebody shall have found out what a genus and a species are really, 

 then the systematizers' work will be over and the weary student will 

 rest. Until that happy time, as it seems to me, the object of a syste- 

 matist should be to avoid excessive differentiation, and, at the same 

 time, aim at convenience. The two things are indeed, to some extent, 

 synonymous ; and probably those who are so ready to found species 

 and genera upon " a single specimen," " one specimen not in good 

 order," or even "a single mutilated specimen," are storing up mountains 

 of work for which future students will not thank them. But, taking 

 only what one might call the "tertiary" sub-divisions of insects (that 

 is, the divisions of Families), it would seem that the first main character 

 to be fixed on should be one which is readily visible, organic, and 

 constant, and it must be peculiar to the sub-division. 



Thus, for example, amongst Coccids, a covering, waxy, cottony or 

 felted, would not suffice, for it is neither constant nor confined to any 

 group ; loss of antennae or of feet would be similarly insufficient, for 

 examples of either can be found in both Diaspidce and Goccidee. But, 

 as remarked in my paper of 1883, there is one (double) character quite 

 distinctive of the Lecanidce, namely, the presence of an abdominal 

 cleft with two small dorsal lobes. Mr. Morgan confines himself, I see, 

 to the discussion only of the " lobes " as against the " anal tubercles " 

 of Goccidee. I have not done so. I am not prepared to say that 

 Mr. Morgan is wrong in his idea that, throughout the whole Family, 

 the anal tubercles'may be taken as existing with various modifications ; 

 morphologically he may be right, but I have not studied the point. 

 But, taking them in combination with the " abdominal cleft," there is 

 no species of Lecanid, as far as my observations extend (and I have 

 examined many genera beside the New Zealand forms), in which the 

 two together cannot be made out with close approach to certainty. 



I will go farther. Allowing that the " lobes " in Lecanid larvae 

 are, proportionately, larger than those of the adult, yet in my experi- 

 ence, I know of no case where they project beyond the anal edge of 

 the body. I have before me, as I write, a microscopic slide, prepared 

 by me in 1877, of Lecanium liesperidum taken from a myrtle bush. The 



MM 2 



