Folds of Epidermis 



37 



seen towards tlie middle of each segment ; in other places, 

 such as at the fore part of the prothorax, at the junctions 

 of the segments, or in the anal blood-gills, they take the 

 form of an undifferentiated layer of protoplasm, in which 

 nuclei lie scattered. In these situations no cell-divisions 

 can be made out either in the living larva or in sections ^. 

 The protoplasmic layer is here very unequally distributed, 

 being often drawn out into irregular internal processes. 



Fig. av— Internal elevations or thickenings of epidermis, as seen in dorsal 

 wall of prothorax of living larva, surface view. 



In the anal blood-gills it attains its greatest thickness, 

 and here the large nuclei, thinly covered by protoplasm, 

 bulge into the blood-cavity. 



The epidermis often exhibits small folds which do not Folds of 



affect the chitinous cuticle outside. They become parti- 

 cularly evident shortly before a moult. At such time 



ex^iderniis. 



Fig. 26.— Section through dorsal wall of prothorax, showing thickenings 

 of undifferentiated epidermis, c, cuticle, e, epidermis. 



there may be seen within the transparent blood-gills, for 

 instance, a wrinkled epidermis, whose surface is plainly 

 larger than that of the cuticle within which it lies (fig. 28). 



' A syncytium, or continuous layer of protoplasm witli scattered 

 nuclei, has often been observed in the epidermis of Arthropods, especially 

 in early stages, as also in Rotifera, Gordiidae, &c. See Leydig, 1864 b, 

 pp. 21, 34, and the text-books of Comparative Anatomy. 



