DUBLIN UNIVERSITY BOTANICAL AND ZOOLOGICAL ASSOCIATION. 1 79 



authorities. My object has not been to compile even a complete list of 

 references, but to select such as would be most practically useful, by 

 their intrinsic completeness and accuracy, or as supplemental to one 

 another, paying, in most instances, so much deference to the earliest 

 observers as to cite them, — except when their accounts were so vague 

 as to be quite insignificant, — even though they may have been since 

 almost superseded by more recent and complete observations. As to 

 classification and description, I have gone no further than, following 

 Bouche, to indicate under each family, in a general way, the few broad 

 characters which seem to distribute the larvae into their primary large 

 groups. These characters are partly drawn from the disposition of the 

 Inspiratory system, — the Spiracles being either distributed one at each 

 side of several of the intermediate segments also (Peripneustic), — or 

 limited to the pair of anterior openings in the first segment after the 

 head, and another terminal pair frequently compound (Amphipneustic), 

 — or finally, these last alone remaining (Metapneustic). Next in impor- 

 tance to this we consider the development of a distinct Head, strength- 

 ened by a horny integument, affording a fulcrum for strong muscles 

 which move biting or grinding jaws (Eucephalous) ; — while in a great 

 number the head, or first segment, differs from the following segments 

 not by texture, but merely by its terminal position, and as the seat of 

 the antennae and organs of the mouth; the jaws, in this case, being 

 usually metamorphosed into hooks, with long internal roots, having an 

 alternate motion, and mutually parallel (Acephalous). Such an imper- 

 fect head is usually capable of being wholly withdrawn and concealed 

 within the following segments, whence Bouche has applied to this last 

 description generally the term " Leech-like." Finally, we admit a 

 character of a different nature, and which we may be able to dispense 

 with hereafter, when the organization of the larvae shall have been 

 more closely studied, and comes to be better understood; that is the 

 circumstance, that in many instances tfre skin of the larva is not cast, 

 but contracted and hardened into a case to protect the included pupa 

 (Obtected); while in other instances, as is usual in most orders of insects, 

 the larva-skin splits and shrivels up, the pupa being stripped either 

 partially or completely (Extricated). The spines and other processes 

 found in certain larvae — those being the most remarkable which are 

 subservient to the peculiar economy of the aquatic kinds — appear to be 

 of a slighter systematic moment than the other characters we have spe- 

 cified ; and even the presence of eyes, rare and almost exceptional as 

 it seems to be among the larvae of this order, has not afforded any clue 

 but what is also deducible, simultaneously, from other more obvious 

 appearances. 



For the references to authorities compiled in the following list, I 

 have adopted the same abbreviations, in general, as Mr. Walker has 

 employed in his " Insecta Britannica Diptera," as that work will be 

 almost necessarily in the hands of all who study this order in our own 

 country ; but for the sake of beginners who may not possess the book, 

 I have subjoined the explanation of such references as I have had occa- 



