No. 2.] LINE SYSTEM OF BATRACHUS TAU. 253 



In the researches of Kupffer (36), we gain important addi- 

 tions to our knowledge of the development of the cranial 

 ganglia in connection with the thickenings of the ectoderm 

 which have long been recognized, but little understood. Since 

 Beard's (16) and Froriep's (39) simultaneous discovery of " bran- 

 chial sense organs " in the embryos of sharks, and the corre- 

 sponding transient structures in embryos of higher forms, there 

 has been much controversy in regard to the question of the 

 ectoblast elements entering secondarily into the formation of 

 the cranial ganglia and nerves. There has been much hesita- 

 tion on the part of investigators in accepting this fact, for, as 

 Froriep (39) has said, " It would certainly bring about a 

 fundamental change in our views, were we to be convinced that 

 during a long period of embryonic development, the whole 

 ectoblast possessed the capacity to act as ' Nervenkeim.' " 



It is now settled beyond dispute that these "placodes" in 

 Ammocetes do furnish material to the processes growing down 

 from the neural ridge, and subsequently forming the cranial 

 ganglia and nerves. The peripheral portion of the "placodes " 

 may become the "foundations of the primary sense organs." 

 The sense organs of the lateral line, although distributed over 

 the entire length of the trunk, are connected with ganglia 

 formed in the head region, and are therefore innervated by cranial 

 nerves. There seems every reason for considering the system 

 as belonging with the more highly specialized sense organs. 



In his admirable paper on "The Cranial Nerves of Am- 

 phibia," Strong (11) has shown the extensive modification 

 which takes place in the nervous system of Rana, due to the 

 disappearance of the lateral line organs in the adult, and sug- 

 gests " the importance of taking into full consideration, as a 

 factor, the cutancoits sense 07'gans in the attempt to obtain a 

 philosophical understanding of the changes undergone by the 

 peripheral and central nervous systems. The development 

 and specialization of these structures have probably played an 

 important part in the changes leading to the organization of 

 the vertebrate peripheral and central nervous systems." 



University of Chicago, 

 May, 1896. 



