DEVELOPMENT OF CUCUMARIA ECHINATA 908 
longer and have removed near to the posterior end (p,, 5). Thus, 
as compared with the doliolaria, the ventral surface has very 
much extended. The mid-ventral radial canal is still the largest 
of the five radial canals ; the other four do not as yet reach the 
posterior end of the body. Muscular layers of the ring, radial, 
tentacular, and pedicel canals have much developed and are 
well distinguishable, but no fibres are as yet visible in the 
Polian vesicle. The pore-canal still opens to the exterior through 
the body-wall. 
Almost at fhe end of the stage, on the tenth day, the third 
pedicel appears on the left side of the mid-ventral radial canal at 
about the middle of the body (Text-fig. 7, p3). It is much smaller 
than the primary pair, and, like the subsequent members, 
develops directly above the body-surface without forming at 
first any sort of pedal pit as met with in the primary pair. 
Ludwig (22, p. 186) found a similar condition in the forty- 
fifth-day young of C. planei, and deseribed a rudiment of the 
ampulla projecting into the body-cavity. I could not make out 
any ampulla in the early stage. 
Alimentary Canal.—tThe gut has now become an open 
canal beginning at the mouth to end in the anus. The pharynx 
seems to originate from the endoderm, the atrial wall forming 
only a very beginning part of the canal. The wall has become 
quite thin, and the internal lumen widened remarkably. Circular 
muscle fibres are found only at the pharyngeal part, the other 
part forming no such structure as yet. The intestine now 
shows a characteristic coil in accordance with the peculiar 
arrangement of the mesentery. - 
The corresponding stage was observed by Danielssen 
and Koren in C. frondosa, and by Kowalewsky in 
Phyllophorus urna. The larvae in both forms had 
five tentacles and a pair of the primary pedicels. Ludwig 
(28, p. 26) observed the pentactula of C. parva found in the 
brood-pouches, measuring 0:5-0-6 mm. by 0-28-0-31 mm. 
The five tentacles showing no trace of ramification, a pair of 
the primary pedicels, gut, stone-canal, calcareous ring, and eal- 
careous deposits of integument are described. A very interesting 
