THE CRANIAL GANGLIA IN AMEIURUS 



365 



regions. This portion of the ganglion was never attached to the 

 epidermis at this point, but has grown backward and upward 

 from the points indicated in the two preceding figures. The gan- 

 glion has now become longer than its point of attachment to the 

 epidermis. Fig. 60, 93 hours, illustrates the first stage in which 

 the epibranchial ganglion of the IXth is first completely detached 

 from the epidermis. This section is taken through the point 

 where the ganglion lies nearest the epidermis, i.e., near the anter- 

 or border of the ganglion. Careful measurements of the length 

 of the ganglion and of its point of attachment in a series of stages 

 make it evident that the ganglion grows as indicated. 



TABLE III 



Showing the relative length of the epibranchial ganglion of the IXth as compared with 

 the length of attachment (A. melas). 



Age in hours 



Length of attachment to placode in 



sections 



Length of epibranchial ganglion in 



sections 



113 







15 



In the first series (69 hours) the mesially projecting mass is no 

 longer than the thickening, but in the following series the gan- 

 glion occupies seven sections and the attachment two. In the 

 later stages the ganglion elongates rapidly up to 99 hours, where 

 it is twenty-five sections in length, and after that, owing to its 

 becoming placed in a dorso-ventral position, is not so long. In 

 an embryo of 93 hours the ganglion is not in contact with the skin, 

 but is found in contact in two later series, 99 and 105 hours, and 

 after 113 hours it is permanently detached. The placode does 

 not present the appearance of adding cells to the ganglion after 

 the 93-hour series. The anterior end of the ganglion seems to be 

 simply lying in contact with the epidermis which no longer re- 

 sembles a placode. The epidermis has not yet resumed its normal 

 appearance, but shortly after this stage there is nothing in the 

 character of the epidermis to indicate the point at which the gan- 

 glion arose. 



