STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 759 



resemble the horny fin-rays in the fins of embryo Elasrno- 

 branchs in their development and structure. They appear 

 gradually to enlarge to form the permanent rays, and we have 

 followed out some of the stages of their growth, which is in 

 many respects interesting. Our observations are not, however, 

 complete enough to publish, and we can only say here that their 

 early development and structure proves their homology with 

 the horny fibres or rays in fins of Elasmobranchii. The skin is 

 still, however, entirely naked, and without a trace of its future 

 armour of enamelled scales. 



The tail of a much older larva, 1 1 centims. in length, in 

 which the scales have begun to be formed, is shewn in Plate 34, 

 fig. 1 6. 



We complete this section of our memoir by quoting the 

 following passages from Agassiz as to the habits of the young 

 fish at the stages last described : 



" In the stages intervening between plate iii, fig. 19, and 

 plate iii, fig. 30, the young Lepidosteus frequently swim about, 

 and become readily separated from their point of attachment. 

 In the stage of plate iii, fig. 30, they remain often perfectly quiet 

 close to the surface of the water; but, when disturbed, move 

 very rapidly about through the water. . . . The young 

 already have also the peculiar habit of the adult of coming to 

 the surface to swallow air. When they go through the process 

 under water of discharging air again they open their jaws wide, 

 and spread their gill-covers, and swallow as if they were choking, 

 making violent efforts, until a minute bubble of air has become 

 liberated, when they remain quiet again. The resemblance to a 

 Sturgeon in the general appearance of this stage of the young 

 Lcpidostcus is quite marked." 



BRAIN. 

 I. Anatomy. 



The brain of Lepidostcus has been figured by Busch (whose 

 figure has been copied by Miklucho-Maclay, and apparently by 

 Huxley), by Owen and by Wilder (No. 15). The figure of the 

 latter author, representing a longitudinal section through the 



