488 ' Simon Henry Gage 



A-C. (X 12.) At the left. Papillae from the circumoral fringe of the 

 brook lamprey. A is from the meson at tlie cephalic edge, B from the 

 side, and C from the meson at the caudal edge of the disc. 



Fig. 22. (X i6). Ventral view of the head of a larval lamprey 135 

 millimeters long to show the ventral lip, the upper or dorsal hood-like 

 lip, and the branched tentacles forming a sieve over the entrance to the 

 mouth. In this figure the tentacles are somewhat unnaturally separated. 

 During life they are more closely approximated, thus making a fine 

 strainer to prevent the entrance of coarse particles into the branchial 

 cavity. By comparing with figure 41 of plate vii, the entire tentacle 

 will be seen to resemble a cauliflower somewhat. 



D. L. Dorsal lip or hood. It embraces the lateral extensions of the 

 ventral lip. 



L. T. The ventral median tentacle which may be designated the 

 lingual tentacle as it is supposed to be an important factor in the for- 

 mation of the adult tongue. 



V. L. Ventral lip. Its lateral extensions are entad of the dorsal lip. 



Fig. 23. (X 16). Ventral view of the head of a transforming larva, 

 to show the narrowing of the head and mouth at this stage, and also 

 the arrangement of the tentacles around the oral disc, as if they were 

 to be transformed into the future teeth. The union of the dorsal and 

 ventral lips to form the circular, oral disc is also shown. 



D. L. and V. L. The dorsal and ventral lips in the process of fusing. 



L. T. The tongue which appears to be derived largely from the me- 

 dian lingual tentacle. Compare figure 22. 



Fig. 24. (X 3"). Annular cartilage of a lake lamprey, to show the 

 form of the cartilage and the position of the supra- and infra-oral teeth. 



F. Foramen opening into the interior of the cartilage. There is 

 something of an angle at the point of entrance of the foramina 

 and the general appearance is strikingly like the jaws of a shark. 



/. L. Infra oral or mandibular teeth. There were nine in this speci- 

 men, eight in the one represented in figure 19. 



5. L. Supra-oral lamina or maxillary teeth. 



Fig. 25. (X 2)^). Annular cartilage and part of the tongue with the 

 lingual teeth of a sea lamprey. The tooth plates are removed from the 

 annular cartilage, thus bringing into view the supporting eminences of 

 cartilage for each tooth. 



F. Foramen near the middle of the annular cartilage. 



/. L. Infra-oral or mandibular tooth supports. 



L. T. Lateral lingual teeth. There are thirteen on the right and but 

 ten on the left. Ordinarily the lateral variation is not so marked. 



S. L. Supra-oral or maxillary tooth supports. 



T. Part of the tongue. 



V. L. Ventral lingual lamina. Compare the ventral lingual tooth- 

 plate in figures 19-20, and 2i. 



Fig. 26. 'X 7). Animlar cartilage of the brook lamprey. 



F. Foramen leading to the interior of the cartilage. Compare the 

 same in figures 24, 25. 



/. L. Infra-oral lamina supported by the ventral half of the annular 

 cartilage. 



S. L. Supra-oral lamina or maxillary tooth-plate supported by the 

 dorsal half of the annular cartilage. This plate is in marked contrast 

 to those of the lake and sea lamprey, where the maxillary teeth are very 

 close together. Brook lampreys are occasionally found with one or 

 more intermediate teeth on the supra-oral lamina. (Jordan, '82, '85.) 



