No. 2.] LINE SYSTEM OF BATRACHUS TAU. 229 



ficial. There is a direct union of the canals of the two sides 

 of the head between the eyes, but no organ is developed in 

 this commissural portion (Fig. 23; also Fig. 4). 



Pores. 



For a complete understanding of the relation of the pores 

 to the canals, a knowledge of their mode of development is 

 necessary. Each organ becomes enclosed in a short canal 

 (Cut I), the two openings of which are called by Allis terminal 

 or half pores. By the union of these half pores, the so-called 

 primary pores of the young Amia are formed. 



In the case of Amia there is a subsequent process of division 

 of these primary pores, resulting in the dendritic systems of 

 the adult fish. The pores in Batrachus correspond to the 

 terminal and primary pores of Allis, as shown in the diagram 



'z 6 -^ rf 



Cut I. — Diagrammatic representation of the formation of a primary pore : <z, b, and r, two 

 terminal pores approaching each other and fusing ; d, primary pore. 



representing the post-larval stage of Amia. (Compare Figs. 

 21 and 22.) In the supraorbital line of Batrachus the primary 

 fores have become fused, so that only the two terminal pores 

 are present, and no pore marks the union of the canals between 

 the eyes, as seen in Cottus gobio. These pores, in process of 

 fusion, may be observed during the development of the canals 

 in the young fish. 



It seems all-important that the term/^;r be restricted in its 

 application to the openings into the canals. In consequence of 

 the indiscriminate use of this word, it is often difficult to under- 

 stand the statements of some writers. A puzzling case is pre- 

 sented in a description of the canals of Polyodon by a writer (6) 

 on the Sensory System of Ganoids, where the '' cluster pores" 

 are described as openings of canals, and figured as sense organs ! 



A recent writer (7) in alluding to this subject says: "The 

 word pore is inappropriate in Amphibia if used in the same 



