No. 2.] LINE SYSTEM OF BATRACHUS TAU. 25I 



in Iijghcr forms." This is a complete description of the course 

 of the R. reciirrens facialis in Batrachus. 



9. Amphibia. — While Batrachus is a true teleost, there are 

 certain superficial resemblances to the Urodeles, the sense 

 organs of both having much the same appearance and arrange- 

 ment on the body. 



As regards the course of the cranial nerves, Strong (11) 

 has pointed out the remarkable homologies that are presented 

 in the tadpole and the teleost ; the dorsal branches corre- 

 sponding to those of teleosts being present in the tadpole but 

 becoming aborted in the adult frog. 



General Summary. 



Development of organs and canals. — The sense organs of the 

 lateral system in Batrachus arise from special cords of cells 

 formed in the lower layer of the epidermis. These cords origi- 

 nate from certain thickenings which make their appearance in 

 the auditory region of very young embryos, and proliferate 

 along definite lines on the head and trunk. The enlarged 

 growing end of one of these cords pushes its way from the 

 auditory region to the e.xtreme posterior part of the body, 

 the swollen appearance remaining conspicuous for some time 

 in the region of the caudal fin. 



These thickenings of the ectoderm give rise to the sense 

 organs ; each organ arising as a " local proliferation " of cells 

 along the cord (Fig. 15). These cells push through the over- 

 lying epidermal cells and gradually take on the form and char- 

 acter of the adult organ, having the hair cells well developed, 

 and the so-called "cupola" structure surmounting the organ. 



In a later stage each organ sinks slightly below the surface, 

 and a pointed fold of the skin projects on either side of it. 

 This is the permanent condition of the majority of the sense 

 organs of Batrachus. On each side of the head, however, four 

 short canals are formed. They enclose organs identical with 

 those remaining on the surface, and the canals may be regarded 

 as a fusion and extension of the paired flaps which serve to 

 protect the free organs. In the adult the canals lie in open 



