176 THE MICROSCOPIST. 



classification (Plate XVII, Fig. 132). Thus in the Cole- 

 optera we have the Serricornes^ or serrated antennae; the 

 Clavicornes, or clubbed ; the Palpicornes, with antennae no 

 larger than palpi ; the Lamellicornes, with leaf-like appen- 

 dages to the antennae ; and the Longicornes, with antennae 

 as long or longer than the body. Xerve-fibres, ending in 

 minute cavities in the antennae, have been traced, which 

 are supposed to be organs of hearing. The antennae should 

 be bleached to exhibit them. The bleaching process is 

 also useful for other parts of insects. The bleaching fluid 

 consists of a drachm of chlorate of potass in about two 

 drachms of water, to which is added about a drachm of 

 hydrochloric acid. 



Compound eyes of insects are always interesting. They 

 are quite conspicuous, and often contain thousands of 

 facets, or minute eyes, called ocelli (Plate XVII, A B, Fig. 

 133). Besides these, insects possess rudimentary single 

 eyes, like those of the Arachnidce. These are at the top 

 of the head, and are termed stemmata (Plate XVII, a, 

 Fig. 133). To display the " corneules," or exterior layer 

 of the compound eye, the pigment must be carefully 

 brushed away after maceration. A number of notches 

 may then be made around the edge, the membrane flat- 

 tened on a slide, and mounted in balsam. Vertical sec- 

 tions may be made while fresh, so as to trace the relations 

 of the optic nerve, etc. The dissecting microscope and 

 needles will be found useful (Plate XVII, Fig. 132). 



Mouths of insects present great varieties. In the beetles 

 the mouth consists of a pair of mandibles, opening later- 

 ally ; a second pair, called maxillae ; a labrum or upper 

 lip ; an under lip or labium ; one or two pairs of jointed 

 appendages to the maxillae, termed maxillary palpi ; and 

 a pair of labial palpi. The labium is often composed of 

 distinct parts, the first of which is called the mentum or 

 chin, and the anterior part the ligula or tongue. This 

 latter part is greatly developed in the fly, and presents 



