376 F. L. LANDACRE 



sert that we had a true placode here. However, I believe that 

 the contact of the lateral mass ganglion with the epidermis is 

 purely a secondary matter and that while it cannot be proven, 

 in all probability the fifth epibranchial placode is contributing 

 cells to the lateral mass ganglion. I can see no other interpreta- 

 tion for the presence of the early stage of the placode before the 

 contact, or the persistance of the contact during the time usually 

 occupied in the proliferation of cells from the placode. As men- 

 tioned above, however, I have been unable to separate this gan- 

 glionic mass into lateral mass and placodal portions. 



Fig. 72 is taken through the middle of the fifth epibranchial 

 placode of a 99-hour embryo. The attachment of the lateral mass 

 to the placode is here slightly anterior to the anterior end of the 

 lateralis Xth, which does not appear in the figures. Fig. 73 is 

 from an embryo of 105 hours. The lateralis Xth and lateral mass 

 are cut through the anterior portions. The placodal thickening 

 is seen to extend ventrally in the epidermis as do those of the sec- 

 ond, third and fourth placodes. The attachment to the epidermis 

 does not continue up to the 113-hour stage, and judging by the 

 distance of the ganglion from the epidermis in this stage may dis- 

 appear some time before this, perhaps between the 105 and 113- 

 hour stages. 



The sixth epibranchial placode is less prominent than the fifth. 

 The lateral mass ganglion retains its contact a shorter time with 

 the epidermis, which is slightly thickened, and I have not been 

 able with certainty to identify the placode previous to the time the 

 contact is formed. The series from which I describe it are taken 

 from 6 to 8 hours apart, and this is not sufficiently close to be sure 

 that the placode is not visible before the time of contact of the 

 lateral mass with the ectoderm. 



In an embryo of 113 hours there is present a second contact 

 between the lateral mass cells and the epidermis. This contact 

 occurs at the posterior end of the lateral mass portion of the Xth 

 ganglion, which is quite large at this time and extends back of the 

 fifth gill slit. The contact is present in an embryo of 113 hours 

 from which fig. 74 was drawn, and must have been formed earlier 

 but does not continue as long as the 120-hour stage. I have been 



