222 WIXTERTON C. CURTIS. 



PLATE IV. 



Figures showing stages in the proglottid formation of C. laciniatum as found in 

 the spiral valve of the shark, Carchaiias littoralis. All from camera lucida outlines. 

 The magnification is given for the figures as reproduced. 



FIG. I. The youngest specimen obtained. The outline at the posterior end indi- 

 cates that at least one proglottid has been lost, but the small size of the scolex shows 

 that this one is slightly younger than the complete specimen shown in Fig. 2 and 

 hence it is unlikely that more than one proglottid is missing. < about 50 diameters. 



FIG. 2. A complete specimen slightly older than that of Fig. i. The first pro- 

 g'.ottids are forming from behind forwards in typical cestode fashion. ( about 50 

 diameters. 



FIG. 3. The posterior region of a specimen in about the stage of Fig. 2, show- 

 ing a very long terminal proglottid which is bent in two places, but does not show any 

 lines of division. Compressed when killed and hence apparently wider than Fig. 2. 

 ( 18 diameters. 



FIG. 4. A similar specimen showing a condition which suggests that a long termi- 

 nal proglottid of an earlier stage has begun to divide into two. < 18 diameters. 



FIG. 5. A specimen slightly older than Fig. 2. The scale of 50 diameters being 

 the same as that of Figs. I and 2 shows the marked increase in size. X 5 diameters. 



FIG. 6. Posterior portion of a specimen somewhat older than Fig. 5- To show 

 typical dimensions of proglottids at this stage. The last division line is faint as though 

 a longer terminal proglottid had just divided. X r & diameters. 



FIG. 7. An entire specimen in which the "anterior proglottids" are appearing. 

 This is actually much larger than the specimen shown in Fig. 5. X *S diameters. 



FIG. 8. The anterior segments of a specimen which still showed an extensive non- 

 segmented zone. >< 42 diameters. 



FIG. 9. The last six segments from the posterior end of a specimen similar to the 

 one used for Fig. 8. X 4 2 diameters. 



FIG. 10. A specimen of about the same stage as Fig. 7, but with fewer " anterior " 

 and more " posterior " proglottids. A deeper constriction is noticed between the 

 eighth and ninth proglottids from the posterior end. -(18 diameters. 



