JOURNAL OF ENTOMOLOGY AND ZOOLOGY 37 



by Mi all and Denny (1886) for Gryllus, and by Matheson (1912) 

 for Corydalis, they are seen to differ. Instead of being lined with 

 a layer of epithelial cells, each tooth is comparativ^ely solid (Fig. 

 6, Tl.), and the epithelium only slightly projects into the base of it. 

 (Fig. 6, Ep.) Matheson found the centre of the teeth of Cory- 

 dalis to be filled with a "supporting tissue" which was non-cellular 

 and considered by him to be a secretory product of the epithelial 

 cells. 



Some of my sections showed clearly that the teeth of Hydro- 

 psyche are formed partly by a secretion and partly by a transfor- 

 mation of the protoplasm. At first there is a layer of chitin sur- 

 rounding a process of the underlying epithelial cells which extends 

 up to the apex of each tooth. (Fig. 5, Cy.) Later, the cyto- 

 plasm becomes transformed into chitin, leaving the fully formed 

 tooth solid. (Fig. 6.) This supports the view that chitin may be 

 formed by a combination of a secretory product of the epithelium 

 and a transformation of protoplasm, rather than by either of these 

 methods considered alone. 



B. The EpitheVnim. The epithelium underlying the teeth pre- 

 sents a wavy outline when seen in cross-section (Fig. 6, Ep.), due 

 to the fact that the cytoplasm extends slightly into the base of each 

 tooth. The nuclei are very prominent and are oval to spherical 

 in shape. Typically, there is one nucleus underlying each tooth, so 

 that they are quite far apart. In a few cases, however, there 

 appear to be two nuclei for a tooth, but this is probably due to the 

 way in which the section was cut. 



The epithelium in the posterior part of the proventriculus is flat- 

 tened, and the nuclei, which are about one-fourth the size of those 

 preceding, are spherical and lie close to one another. (Fig. 4.) 



A slight distance in front of the point where the fore-intestine 

 joins the mid-intestine, the epithelium becomes invaginated into the 

 lumen of the canal, forming the two valves above mentioned. These 

 are covered by a very thick chitinous layer. The epithelium is 

 much flattened on the side toward the lumen, but is composed of 

 columnar cells on the side facing the wall of the enteron. (Fig. 

 4, 7, Ep. col.) 



