240 CLAPP. [Vol. XV. 



The branches of this system on the head also show this 

 peculiar fold (Cut 3), the significance of which it is hard to 

 discover. In connection with this fold, Mitrophanow (15) 

 describes the formation of canals, but gives no figures that 

 illustrate the manner of their formation. Behind the dorsal 

 fin, as seen in older embryos, the "pocket" becomes greatly 

 elongated, and suggests the existence of a canal in that region, 

 but furnishes no clew to the condition that is supposed to exist 

 in the anterior part of the body of the adult Acanthias. Cut 

 4 is a cross-section of the anterior part of the line at this stage. 



Cut 3. — Acanthias embryo, 22 mm. in length. 



This subject has not been sufficiently investigated to afford a 

 satisfactory basis for comparisons. Beard (i6) mentions this 

 growing end of the line as " plowing its way backward through 

 the indifferent ectoderm." The appearance of the structure 

 in Acanthias would suggest this idea. 



Balfour (17) describes the lateral line of Syllium as appearing 

 " in the form of a linear thickening of the inner row of cells of 

 the external epiblast on each side, at the level of the notochord." 

 He says that at this time it shows no segmental character, and 

 he also notes the interesting fact of the "broadening at the 

 growing point." He probably has reference to this remarkable 

 fold of the epiblast when he speaks of the "perfectly abrupt" 

 termination of the line. He also mentions the contrast between 

 the narrow anterior and the broad terminal portion of the line. 

 This thinning out of the anterior portion of the lateral line is 

 noticeable in Batrachus. Allis describes and gives figures of 

 surface preparations showing the same appearance of the line in 

 Amia. " The ends of these lines are enlarged, that of the 

 lateral line sometimes forming a large and prominent swelling." 



Hoffmann (18) regards the sense organs as arising seg- 

 mentally, and gives no account of the growth of the rudiment 



