STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 755 



prominent, and the papillae (about 30 in number) covering it are 

 more conspicuous from the surface. It is not obviously com- 

 posed of two symmetrical halves. The opercular flap is larger, 

 and the branchial arches behind it (two of which may be made 

 out without dissection) are more prominent. 



The anterior pair of limbs is now visible in the form of two 

 longitudinal folds projecting in a vertical direction from the 

 surface of the yolk-sack at the sides of the body. 



The stages subsequent to hatching have been investigated 

 with reference to the external features and to the habits by 

 Agassiz, and we shall enrich our own account by copious quota- 

 tions from his memoir. 



He states that the first batch were hatched on the eighth 1 

 day after being laid. " The young Fish possessed a gigantic 

 yolk-bag, and the posterior part of the body presented nothing 

 specially different from the general appearance of a Teleostean 

 embryo, with the exception of the great size of the chorda. The 

 anterior part, however, was most remarkable ; and at first, on 

 seeing the head of this young Lepidosteus, with its huge mouth- 

 cavity extending nearly to the gill-opening, and surmounted by 

 a hoof-shaped depression edged with a row of protuberances 

 acting as suckers, I could not help comparing this remarkable 

 structure, so utterly unlike anything in Fishes or Ganoids, to the 

 Cyclostomes, with which it has a striking analogy. This organ 

 is also used by Lepidosteus as a sucker, and the moment the 

 young Fish is hatched he attaches himself to the sides of the 

 disc, and there remains hanging immovable ; so firmly attached, 

 indeed, that it requires considerable commotion in the water to 

 make him loose his hold. Aerating the water by pouring it from 

 a height did not always produce sufficient disturbance to loosen 

 the young Fishes. The eye, in this stage, is rather less advanced 

 than in corresponding stages in bony Fishes ; the brain is also 

 comparatively smaller, the otolith ellipsoidal, placed obliquely in 

 the rear above the gill-opening. . . . Usually the gill-cover is 

 pressed closely against the sides of the body, but in breathing an 

 opening is seen through which water is constantly passing, a 



1 This statement of Agassi/ tides not correspond with the dates on the specimens 

 >ent to us a fact no doubt due In the hatching not taking place at the same time for 

 all the larva.-. 



