410 Edward Phelps AUis jr., 



anterior and next posterior sections. Dorsal to this organ, tlie canal 

 begins again, and slightly dorso-posterior to the eye turns directly 

 backward and so continues until it joins the lateral line of the body. 

 In that portion of the suborbital part of the canal that lies anterior 

 to the unenclosed organ, there were, in the specimen sectioned, twelve 

 sense organs. Then followed the one sense organ not yet enclosed, 

 and dorsal to that organ, between it and the bend in the main canal, 

 still another organ, which latter organ is the most dorsal one of the 

 postorbital series. This latter organ is thus enclosed in a section of 

 canal which is, at this age, continous with the squamosal canal but 

 not continuous with the more anterior portion of the infraorbital canal, 

 resembling exactly, in this, that section of the same canal, that, in 

 Amia, encloses the postfrontal organ. And, notwithstanding that the 

 innervation of the organs in Lepidosteus was not determined, the 

 organ here under consideration is certainly the homologue of the post- 

 frontal organ of Amia. Posterior to this postfrontal organ of the larval 

 Lepidosteus the first three infraorbital organs lie in the squamosal, 

 two lying anterior to the point where the canal anastomoses with the 

 dorsal end of the preopercular canal, and one posterior to that point. 

 The next posterior organ is enclosed in the lateral one of the two 

 extrascapular bones usually found on each side of the head of the 

 fish; and it is the last organ shown in my reconstruction. 



The supratemporal canal, on either side, is just being enclosed, 

 and the two canals do not as yet meet in the middle line. The 

 number of organs in this canal is not shown in the reconstruction. 



The preopercular canal is just anastomosing, at its dorsal end, 

 with the main infraorbital. 



What is apparently a middle head line of pit organs is quite 

 distinctly shown in the drawings, and also what is apparently an 

 anterior head line; but this latter line may be simply a surface 

 marking. There is no indication whatever of a posterior head line. 

 None of these lines are shown in the reconstruction. 



In the adult Lepidosteus the primarily simple primary tubes of 

 larvae have undergone repeated dichotomous subdivision, and the 

 branches of the dendritic systems so arising have anastomosed and 



