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E. A. ANDREWS. 



of preservation but is based upon a special arrangement of the epi- 

 dermis, which, Fig. 7 enlarged two hundred diameters, is a single 

 layer of polygonal cells, close under the cuticle. This layer dips 

 down under the groove and on the side of the groove, where seen 

 in profile, the cells are elongated and continued as fine fibers that 

 connect with connective tissue cells and with a membrane sepa- 

 rating the epidermis from the large blood sinus just above it. 

 In the figure these cells are represented in black as seen in opti- 

 cal section and also represented as seen in surface view upon 

 another focus. Posteriorly the epidermis had shrunken away from 

 the cuticle, in preparation, and left a wide artificial space. In an 

 actual cross section of this region the groove is found to be just 

 below the posterior part of the ganglion, Fig. 8, that supplies the 

 fifth pair of legs, so that one might argue that the annulus be- 

 longed to the last thoracic somite while lying in the penulti- 

 mate one. As seen in Fig. 8, which is enlarged two hundred 



FIG. 8. 



diameters, the epidermis cells fit together as polygons only at their 

 outer ends next the shell while their inner ends taper off as fibers 

 which diverge right and left of the central part of the groove. 

 The epidermal cells are thus stretched out laterally and arranged 

 on each side with reference to the superficial median groove that 

 is to become the sperm receptacle. 



Enclosing the epidermal cells is a coagulum of blood partly 

 separated by a membrane from the blood space beneath the nerve 

 cord. In this space lies the large median ventral artery that 

 anterior to this section connects through the nerve cord with the 



