II02 BULLETIN OF THE BUREAU OF FISHERIES. 



As clearly as I can determine (artificial fertilization not having been possible) , 

 the bursting of the shell takes place eleven days after fecundation. Ryder 

 (1887) says that on Chesapeake Bay the incubatory period lasts from ten to 

 fifteen days. According to Patterson (quoted in Osburn's letter to the writer) : 

 "In 1906 young fish at Woods Hole broke the capsule in twenty-six days." 

 The difference in the time of hatching at Woods Hole and Beaufort is plainly 

 due to the difference in temperature of the water, the higher temperature at the 

 latter place greatly hastening development. 



Figure 7, plate ex (one-half natural size), shows one-half of a nest of eggs 

 in the early larval stage. Whether it is a photograph of the shell shown in 

 figure 3, plate cviii, I can not say positively, since my records are not clear on 

 this point, but I believe that it is. The tadpole-like appearance of the young 

 spoken of by writers is very apparent. As in most shell nests at this stage the 

 embryos point in one general direction, but toward the hinge rather than the 

 opening of the shell, and consequently away from instead of toward the light, 

 as Ryder (1886 and 1887) positively asserts. 



Figure 8, plate ex, shows the same board nest shown in figure 5, plate cix, 

 and represents the larvae in natural size and in a stage of development slightly 

 older than the preceding. Here the embryos point in all directions, as stated 

 in the first part of this paper. The tadpole-like structure is very apparent, 

 due to the broad, flat head with its opercular flaps, just back of which are the 

 pectoral fins, the largest organs with which the fish is provided at this stage of 

 its development. 



There may be plainly seen in this figure the empty shells still adhering to 

 the nest. The eggs have either died and been removed to prevent the spread of 

 disease or they have been taken away for preservation in alcohol for further 

 study. The empty shells with the adhesive disks are very resistent to decay, 

 but finally the gluey substance by which they are affixed becomes loosened 

 and they may readily be removed. 



The pectoral fins have been referred to. Their formation precedes in time 

 and position the formation of the pelvics. These latter originate at this period 

 as two folds just back of the pectorals. As the fish develops these become 

 "translocated," as Ryder (1886) puts it, to their permanent jugular position. 

 Both Ryder (1887) and Miss Clapp (1899) have figures of the just-hatched 

 toadlet which show these fins and also make clear the fact that there is no 

 definite caudal fin at this stage. Miss Clapp's admirable drawing of this stage 

 has, however, three serious defects, i. e., the larva has neither mouth nor gill slits, 

 both of which in a very rudimentary condition are present, and the extremity 

 of the tail turns downward instead of upward, as Ryder correctly shows. 



Under favorable conditions the embryos make steady progress. The head 

 and mouth parts grow more perfect, the gill covers and pectorals become more 



