The Lake and Brook Lampreys of Nezv York 487 



Fig. 16. (About Jd natural size). A male sea lamprey 575 millime- 

 ters long at the spawning season. The dorsal ridge is very low and the 

 two dorsals are separated by a considerable interval. The eyes were 

 sunken and obscured during the preservation. 



Fig. 17. (vSomewliat less than l<\ natural size.) A female sea lamprey 

 645 millimeters in length at the spawning season. The eggs had not 

 3et l)een shed, hence the fullness of the abdomen. Opposite the first 

 dorsal fin the roundish white mark indicates the place where another 

 lamprey had attached itself to this one. The incompleteness of the 

 tail on the ventral margin is due to some accident either before or after 

 death. 



Fig. 18. (Natural size). Ventral view of the head of the male lam- 

 prey shown entire in figure 16. To show the arrangement of the sen- 

 sory or nerve papillae (see Fig. 20 and 51, PI. VI and VIII). The cir- 

 cumoral fringe or plaiting and the lateral closure of the mouth are also 

 shown. The oblique direction of the branchiopores is shown, especially 

 on one side. 



PLATE VI. FIG. 19-26. 



The mouth and its appendages in the adult, transforming and larval 

 stages. The figures of the adult mouths are from photographs of the 

 fresh specimens made during the spawning season. The other figures 

 are from camera lucida drawings of preserved specimens. The magni- 

 fication of each is given immediately after the number of the figure. 



Fig. 19. (X 2). The ventral aspect of the head of a lake lamprey es- 

 pecially to show the arrangement and number of the teeth. By com- 

 paring the teeth of the supra- and infra-oral laminae with those of the 

 annular cartilage from another specimen (Fig. 24), it will be seen that 

 there are 9 infia-oral teeth on the annular cartilage, and 8 in Fig. 19. 

 The range is from 6 to 10, the most common number being 7 or 8. In 

 rare cases the two supra-oral teeth are fused, thus giving the appear- 

 ance of a single median tooth. 



E. Eye. 



S. O. Sense organs or nerve papillae. For those on the lateral and 

 dorsal aspect of the body, compare figure 51 of plate viii. 



Fig. 20. (X 2). Ventral aspect of the head of a sea lamprey from 

 Lawrence, Mass., to show the oral disc with its concentric rows of 

 teeth, the supra- and infra-oral teeth and the teeth of the tongue. Com- 

 pare figure 25. 



6". O. vSensory organs or nerve papillae. 



Fig 20, A-E. (X 5). Enlarged papillae from the circumoral fringe, 

 to show their size and form at different parts of the circumference. In 

 the lake lamprey the papillae are almost exactly like those here 

 shown, not differing more than the papillae in different sea lampreys. 



A-B. From the fringe at the meson and the cephalic edge of the 

 disc. 



C-D. Papillae from the side of the disc. 



E. Papillae from the meson at the caudal side of the disc. 



Fig. 21. (X 3if). Ventral aspect of the head of a brook lamprey to 

 show the number and arrangement of the teeth. The body opposite the 

 gills is enlarged, as the photograph was taken during the inspiratory 

 phase. The whole dentition is seen to be weak as compared with the 

 lake or sea lamprey. The lingual tooth plate is also markedly different. 



E. Eye. 



6". O. Sensory organs or nerve papillae. 



