No. 2.] LINE SYSTEM OF BATRACHUS TAU. 24 1 



of sense organs on the side of the body. H. V. Wilson (15) 

 has evidently found the line only in the form of a slender cord 

 on the posterior part of the body, and makes no mention of 

 any enlargement at the growing end. From figures in a 

 recent paper on Necturus, by Miss Piatt (19), this enlarged 

 growing point is shown as quite conspicuous. In selachians, 

 ganoids, and amphibia we have evidence of this mode of 

 growth of the sense organ rudiment, but no figures or descrip- 

 tions of the enlarged growing point of the lateral line of any 

 teleost have been published, so far as I am aware. 



Fig. 6 represents the condition of a Batrachus embryo 

 about the time of hatching and when the embryo is still 

 attached to the yolk sac. The principal organs of the different 

 lines can now be distinguished in surface preparations, but a 

 more satisfactory showing of the exact number and position of 

 the organs, as well as of the connecting strand, can be obtained 

 from preparations of the skin, as previously described. 



Regarding the canal and free organs as identical, the devel- 

 opment may be briefly outlined as follows : In Batrachus, as 

 in Amia, the growing line of sensory epithelium begins to 

 present the appearance indicated in Fig. 15, which is a camera 

 drawing from a preparation of the skin at a stage somewhat 

 earlier than that shown in Fig. 6. The cells destined to 

 form the sensory portion of the organ begin to elongate and 

 arrange themselves in a definite manner, suggesting the name 

 " hillock " given by Merkel (20) to this class of organs. At 

 the summit there soon appears a clear vacuolar space toward 

 which the upper portion of the cells is directed. The 

 "hillock" formed in the lower layer of the skin soon pushes 

 its way to the surface and gradually takes on the characteristics 

 of an adult organ. This process has been fully described by 

 Allis (2). 



The sensory and supporting cells are very much alike in the 

 organs of Batrachus, although the cells in the center of the 

 "hillock" are pear-shaped and somewhat shorter than those 

 of the peripheral part of the organ. From Fig. 16, which is a 

 section of a side organ of a fish of one year old, the shape of 

 the adult organ is evidently that of a cone hollowed at the base. 



