THE DEVELOPMENT OF FCHINOCAKDIUM CORDATUM. 483 
fig. 10). These I regard as the first prophecy of the flattened 
spines of the adult. Surrounding' the mouth and alternating 
with the tube-feet are five short inwardly directed spines. 
These I regard as the homologues of the teeth of regular 
Echinoids (dent., figs. 16 and 17). Whilst reserving an account 
of the internal anatomy of the larva for another paper, I may 
say here that sections show that these teeth/^ unlike the 
other spines, have roots which project inwards into dental 
pockets, as do the teeth of regular Echinoids. All the spines 
have thick collars round their bases. These collars consist of 
nervous epithelium, underneath which are the muscles con- 
necting the spines to the plates of the skeleton. 
For a short time there persists a trace of the oral lobe 
of the larva with short stumps representing the I’emnants 
of the antero-lateral and pra3-oral arms and a shallow pit 
repi'esenting the last trace of the larval stomodteum, which 
has become disconnected from the oesophagus (ol., tig. 16). 
Soon, however, this also disappears. Some of the young- 
urchins lived for a week and grew in size. In one of these 
(shown in tigs. 17 and 18) the five first sphgeridia have 
appeared (sidi., fig. 17). These are situated outside the teeth 
in an adradial position, each sph^eridium lying beside a tube- 
foot. These sphaeridia, therefore, cannot correspond to the 
five inter-radial sphaeridia of the adult; the post larval history 
of Echinocardium is quite unknown and a study of it would 
throw light on many important problems. 
In reviewing the life-history which has just been described 
it is evident that we are dealing with a type of development 
much more modified than that of Echinus, and one in which 
the features of the adult appear at a still earlier stage than is 
the case with that genus. 
Imperial Colleob of Science ; 
November 2 7th, 1913. 
