CLASSIFICATION OF GRACILARIA AND ALLIED GENERA. 85 



and emendation, but, broadly speaking, he had a complete grasp 

 of the facts. He first, I think, pointed out the closeness of 

 Gracilaria and Lithocolletis, now universally admitted, and 

 would, I doubt not, had he lived and gained fuller confidence 

 in the value of his own observations, have placed Phyllocnistis 

 along with them. These papers of Chambers are characterized 

 by a philosophical reasoning and careful observation, which will 

 delight those who read them for the first time. 



It is a little difficult by description to give you a clear picture 

 of the specialization that occurs in the structure of these larvae. 



We have been asked, as an exercise in ontology, to consider 

 the experiences and mental attributes that would be possessed 

 by beings possessing only two dimensions and confined thereto, 

 in the same way as we are confined within three. These larvae 

 not only had this question laid before them, but obviously ex- 

 perimented with a view to gain some actual knowledge on the 

 subject. If a steam-roller went over an ordinary caterpillar, it 

 might reduce it to some resemblance to these Gracilariads. 



Their mouth-parts are profoundly altered. They are right 

 away at the anterior angle of a flat triangular head. Each jaw 

 is no longer a biting instrument, but a flat disc hinged at its 

 proximal margin, and working to and fro in its own plane (that 

 of the head and of the larva also), with a serrated margin that 

 acts on anything in front of it like a circular saw. The two jaws 

 may cross one another more or less, but they cut nothing 

 between them ; the cutting is done right in front by each 

 separately. These jaws work between two thin membranous 

 veils, one above and one below them ; these are the labrum and 

 labium. They are finely granulated and spiculated, but possess 

 practically no palpi, no spinneret, nor any other structure, nor 

 are any maxillae to be detected, unless they are represented by 

 certain obscure lines on the jaws. 



In some species the appearance is as though the upper and 

 lower veils were continuous at their margins, thus placing the 

 jaws, as it were, at the mouth of a bag, from which they pro- 

 trude sufficiently to show their cutting edge. Their manner of 

 working suggests that this bag arrangement really exists. 



The larvae live beneath the cuticle of the leaf, which they 

 separate from the parenchyma below by cutting through a row 

 of cells by the circular saw action of the margins of their jaws. 

 The fluid contents of the cells are thus set free, and fall at once 

 into the mouth of the bag. It is probable that the sap is forced 

 towards the oesophagus by the action of the jaws. Being con- 

 fined between the veils above and below, the uncut leaf in front 

 and the moving jaws laterally, it will be subject to a force-pump 

 action like that of certain rotary pumps. 



Chambers (American Ent., 1880, p. 260) deals at some 

 length with the evolutionary questions that are provoked by 



