1 86 ALUS. [Vol. XVIII. 



of ectodermic thickening, while the hyoid portion develops from 

 the hyomandibular ridge. The innervation of the two parts of 

 the line, in the oldest embryo figured (No. 55, Fig. 31), retains 

 the impress of this independence of origin, and agrees strictly in 

 this with the larval and adult conditions found in Atnia. The 

 mandibular line shows, in its development, horizontal and vertical 

 portions separated by a sharp angle; and in the oldest embryo 

 figured, two organs of the line have passed onto the upper lip 

 ventral to the buccal line or organs. The whole arrangement 

 indicates, to me almost unquestionably, a strict analogy with the 

 conditions found in Ainia, and explains, or helps to explain, the 

 somewhat aberrant conditions shown in Chimcera. The dorsal 

 end of the hyomandibular line seems to be shifted forward, rela- 

 tively to the main infraorbital line, in Chimcera, and also in Nec- 

 turus, and a glance at Kingsbury's figures (No. 42) of the sensory 

 lines in other Amphibia will show that this may be a general char- 

 acteristic of all Ichthyopsida other than Teleosts and Ganoids. 



4. Siipratcmporal Commissure. 



The supratemporal commissure lies in the mesial arm of the 

 extrascapular, extending the full length of that arm and then 

 forward and mesially, in the skin, slightly beyond the antero- 

 mesial end of the arm. So far as could be determined, there are 

 only two sense organs in the canal, and hence probably but two 

 dendritic systems in the line. The arrangment of the tubes and 

 pores seems, however, to indicate three dendritic systems. At 

 the antero-mesial end of the line there is a single tube and pore. 

 Posterior to this pore there is a series of from four to seven pores 

 each of which is the external opening of a short tube leading 

 directly into the canal. These tubes and pores are usually ar- 

 ranged in two somewhat separate groups, and one of the two 

 sense organs of the line lies between the two groups. The second 

 sense organ of the line lies posterior to all the tubes, close to the 

 point where the commissure joins the main infraorbital canal. 

 This arrangement of tubes and organs seems to indicate that the 

 terminal system of the line has undergone repeated subdivision, 

 and that the system that normally develops between the second 



