218 LARVAL DEVELOPMENT 
region (Fig. 287), is to be noted the prominence of the 
mouth cavity, and the enlarged gill arches, showing by 
this time the outbudding branchial filaments. In the 
stage of Fig. 288, the larva begins to appear shark-like; 
the fins are longer and more noticeable, the anus has 
appeared, and the branchial filaments by continued growth 
protrude at all gill openings. The external gills thus 
acquired are seen in a later stage (Fig. 289) to have 
disappeared ; they have aided, however, as Beard, Turner, 
and others have shown, in absorbing nutriment, and must 
be looked upon as an especial organ of the larval life of 
the animal. Fig. 289 illustrates a final larval stage: in it 
there appear all of the structures of the adult outward form, 
e.g. shagreen, fin spines, nictitating membrane, anterior 
and posterior nasal openings. This larva has been esti- 
mated to be about a year older than that of Fig. 284. 
Ill. Larval Lung-fish 
The larval history of the lung-fish, Ceratodus, as recently 
described by Semon, seems to offer characters of excep- 
tional interest, uniting features of Ganoids with those of 
Cyclostomes and Amphibians. 
The newly hatched Ceratodus (Fig. 290) does not 
strikingly resemble the early larva of shark (Fig. 284). 
No yolk sac occurs, and the distribution of. the yolk 
material in the ventral and especially the hinder ventral 
‘region is suggestive rather of lamprey or amphibian; it 
is, in fact, as though the quantum of yolk material had 
been so reduced that the body form had not been con- 
stricted off from it. The caudal tip in this stage appears, 
however, to resemble that of the shark, and as far as can 
be inferred from surface views a neurenteric canal persists. — 
Like the shark there then exists no unpaired fin; the 
