E. A. ANDREWS. 



while the spatula and all other lateral outgrowths are absent. 

 Huxley says of A. fliiviatilis, "terminal half of the appendage 

 is really a broad plate, slightly bifid at the summit, but the sides 

 of the plate are rolled in in such a manner that the anterior half 

 bends around and partly encloses the posterior half. They thus 

 give rise to a canal, which is open at each end, and only partly 

 closed behind." In A. leniiisciihis this overlapping of the one 

 part by the other has proceeded much farther, so that in Fig. 14 

 we see the anterior, or median, mass has covered in and concealed 

 the external mass through all the terminal extent. 



In sections this extensive inwrapping becomes at once patent. 

 The section 1 5 shows a widely open canal closed in not only by 

 the rolled median mass but internally by an opposite rolHng of 

 the external mass ; that is, the hypothetical plate, of which the 

 terminal part of the stylet is composed, has both its edges rolled 

 in, first, the external edge and then the median edge outside the 

 other. Both flaps come so close together that near the tip of the 

 canula 1 5 (Fig. 14) the central tube is well shut off from the water 

 (Fig. 15). Contrasting this with Cambarus (Fig. 3) we see that 

 in both cases there is a horny plate inrolled, but in Astacus, this 

 is much like the rolling up of a sheet of paper, while in Cambanis 

 it is the buckling up of a thickened mass whose edges meet over 

 a groove. Cambarus shows the derived, the more special, the 

 less mechanically direct sort of inrolling. 



Farther down the stylet (at 16, 17, 18, of Fig. 14) the rolHng 

 is more and more imperfect (Figs. 16, 17, 18). These figures 

 show the rather thick calcified shell and the usual connective 

 tissue, but the absence of glands is conspicuous. Also the edge 

 of the external mass becomes specialized as a sharp shelf that 

 overarches the large central canal, while the enveloping median 

 mass still overlaps the external mass and makes the closure of 

 the canal a more firm one. 



In Fig. 17 there is a complexity of the canal that exists for a 

 short distance and may prove to be of some significance when the 

 process of sperm transfer can be studied. There is a narrow 

 side-slit from the groove, to the right in the figure, which is made 

 by special thickening of the shell of the external mass. That is, 

 there is a ridge along the bottom of the groove. With this ex- 



