68 CHIRONOMUS PRASINUS. 



by Viallanes, in an important work on the Histology of Insects.* 

 The cuticle is a secreted layer, formed by a secretion from the 

 cells of the hypoderm beneath it. Mr. Lowne, I may mention, 

 considers the cuticle of the Blow-Fly as formed by the coalescence 

 of cells ; t but this view is not, as far as I am aware, supported by 

 any other authority. It is a structureless layer, very thin in young 

 larvae, but thicker and presenting a stratified appearance (see Fig. 

 25), in older specimens. If a larva be crushed beneath the cover- 

 glass in a drop or two of methylated spirit, the cuticle swells out 

 almost immediately to quite ten times its thickness in some places, 

 and the stratification is rendered beautifully apparent; between 

 twenty and thirty stratified lines becoming visible between its 

 inner and outer surface. Underneath the cuticle is a cellular 

 layer, the hypoderm. Each cell of the hypoderm secretes the 

 portion of cuticle immediately above it, and the portions of cuticle 

 thus formed, unite together into a continuous investment. Gegen- 

 baur says that the hypoderm is the homologue of the epidermis 

 in the higher animals, so named from its overlying the dermis or 

 true skin. We must bear in mind that there is no structure in 

 insects comparable to the dermis of Vertebrates, I and that the 

 cuticle does not correspond to any structure found in the latter, 

 whether bearing that name or not, but is a super-added covering. 



The transparency of the cuticle in the larva allows the hypo- 

 dermis to be easily made out in many parts of the integument 

 with a J-inch objective, especially in the thoracic segments, and in 

 the aforementioned respiratory processes on the penultimate seg- 

 ment. A drawing of it is given in Figure 24a,§ and an optical 

 section together with the cuticle somewhat more magnified in Fig. 

 25. It will be observed in Figs. 25 that the central portion of the 

 cells enclosing the nucleus project into the cavity of the ccelom or 



* Recherches sur L'Histologie des Insectes Annales des Sciences Naturelles 

 Zoologie, 6th Ser., torn. 14, 1882. 



t Lowne's Anatomy of the Blow-Fly, p. 10. 



+ I am not aware that any such structure has been recognised. 



_ § Compare Maggot of Blow-Fly, loc. cit,, Fig. 2, Plate XX. Although 

 this- figure undoubtedly represents the condition of the hypoderm as it may 

 be sometimes seen, there are, nevertheless, variations in its appearance, which 

 at present I am unable to explain. 



