486 . Simon Henry Gage 



Fig. 5. (About }d natural size). The first lake lamprey obtained. 

 The branchial apparatus is in the inspiratory phase, and therefore wide- 

 ly expanded. The dorsal ridge, so characteristic of the male lake lam- 

 prey, is more than usually prominent in this specimen ; the fusion of 

 the two dorsal fins is also shown. 



Fig. 6. (| natural size). Part of a male lake lamprey caught in De- 

 cember, to show the decided interval between the two dorsal fins ; also 

 to show the non-appearance of the genital papilla out of the breeding 

 season. The myotomes are also very clearly indicated. 



Fig. 7. (I natural size). Segment of a male lake lamprey in the 

 spawning season, to show that the two dorsal fins appear continuous or 

 simply notched during this season. The genital papilla is also very 

 prominent at this period. 



Fig. 8. (i natural size). Caudal end of a female lake lamprey in the 

 spawning season to show the separation of the dorsal fins even in the 

 breeding season in the female ; the notched appearance of the vent and 

 the fin-like fold extending to the caudal fin. 



Fig. 9. (Natural size). The caudal half of a larval lamprey 150 milli- 

 meters in length, to show the separation of the two dorsal fins. The 

 myotomes are also well shown in part of the length. 



Fig. 10. (Natural size). A small larval lamprey to show the separa- 

 tion of the dorsal fins even in specimens of this size. In specimens 

 only 40 mm. long, there is a notch in the fin showing plainly where the 

 interval is to be. 



PLATE IV. Fig. 11-15. 



Brook Lampreys and a larva just before transformation. 



Fig. 11-12. (Natural size). A pair of brook lampreys taken at the 

 spawning season. Photographed under water with a vertical camera. 

 The male (Fig. 11), has a somewhat prominent genital papilla. In the 

 female (Fig. 12), there is present a marked anal fin-like fold, and the 

 caudal part of the abdomen is full of eggs. In both male and female 

 there is a notch, but no interval between the two dorsal fins, and in the 

 female the cephalic part of the second dorsal is edematous. Compare 

 figure 14. 



Fig. 13. (Natural size). The caudal part of a brook lamprev that 

 had just transformed. The specimen was taken in October, and meas- 

 ured 2GO millimeters in length. The two dorsals are widely separated, 

 but appear to be connected by a very low ridge. 



Fig. 14. (Natural size). An oblique view of the candal part of a fe- 

 male brook lamprey especially to show the edematous second dorsal 

 fin, filling, almost completely, the notch between the two dorsals. Near 

 the end of the spawning season this edema is frequently infiltrated with 

 blood so that the females are marked by a bright scarlet spot. 



Fig. 15. (Reduced i\th). Larval lamprey, 190 millimeters in length, 

 to show the size the larvae may reach before transformation. This one 

 is longer than the adult brook lampreys here figured, but not quite so 

 long as the one from which figure 13 was taken. 



PLATE V. FIG. i5-i8. 



A pair of sea lampreys, from Lawrence, Mass., running up the Merri- 

 mac River to spawn. Photographed under water after preservation in 

 Miiller's fluid. 



