68 PROCEEDINGS OF THE AMERICAN ACADEMY 



feed them on minute fresh-water Entomostraca, I have no doubt they 

 would have continued in excellent condition. During the whole time 

 of the resorption of the yolk-bag, not a single individual was lost. 

 It was only subsequently, when they had been fed for a while on liver, 

 that they showed symptoms of poor condition ; and finally they re- 

 fused to eat it and languished for a few days, although at first they 

 had eaten it apparently with great relish. 



The eggs were laid on the 20th of May ; when they reached Cam- 

 bridge, they were still semi-transparent, the yellowish-green sticky 

 outer envelope measuring about 5 mm in diameter ; the yolk- mass, of a 

 whitish-blue color, was 3 mm . In their general appearance, the eggs 

 resembled those of toads. They were attached to the stones just as 

 they dropped from the females, in groups irregularly arranged or 

 isolated. 



On the 28th of May, the first young Lepidosteus was hatched 

 (Plate I. fig. 1). 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 excep- 

 tion 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 (Plate I. fig. 3), I could not 

 help comparing this remarkable structure, so utterly unlike any thing 

 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 dish, 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 corre- 

 sponding stages in bony fishes ; the brain is also comparatively smaller, 

 the otolith ellipsoidal, placed obliquely in the rear above the gill-open- 

 ing. This is at first a mere small elliptical opening, which subse- 

 quently becomes heart-shaped (Plate I. fig. 11) with the development 

 of the gill-arches, one of which is formed by the anterior part of the 

 gill-opening, while two smaller ones are formed behind it (Plate I. 

 fig. G) much as in Sharks, except that we have a gill-cover in Lepi- 

 dosteus as in bony fishes, which completely hides the gill-arches from 

 view, when seen in profile. It is only when seen obliquely from 



