22 EMBRYOLOGY OF THE STARFISH. Part I. 



from the stomach, from the base of the median anal pair of arms, to the base of the 

 ventral oral arms, thus separating the larva into very distinct dorsal and ventral 

 regions (PL IV. Fig. 4), from the earliest stages of its growth. The body of the 

 larva itself is capable of great motion ; nothing is more common than to see the 

 larvse almost broken in two, by the strange habit they have of bending the oral 

 extremity upon the opening of the motith as a pivot, to such an extent, as to make 

 quite an angle with the anal part (PL III. Fig. 5). The larvaa generally assume this 

 position when disturbed, and usually remain stationary in the same attitude, simply 

 striking violently, up and down with their extremities (compare Fig. 5 and Fig. 2, 

 where the larva is at rest). The whole substance of the body is tinged with yellow, 

 and is« made up of large transparent cells with irregular nuclei, giving the mass 

 about the consistency of a Salpa ; very minute granular epithelial cells cover the 

 whole surface. The powerful contraction of portions of the body is simply that of 

 the cells themselves, and what has frequently been mistaken by Miiller, when de- 

 scribing these larvse, for muscular strise, are strings of such contracted cells. The 

 extremities of the arms are tipped with orange, the stomach and the alimentary canal 

 are of a slight yellowish-brown color, the chords of vibratile cilia are somewhat 

 darker. The oesophagus is perfectly transparent, capable of violent movements ; it 

 expands and contracts by sudden jerks, forcing open violently the passage leading 

 into the stomach, when the contents of the oesophagus rush in, and are set slowly 

 rotating in the stomach. The interior surface of the oesophagus is covered Avith 

 vibratile cilia, so closely crowded that the walls appear striated from the regularity 

 of these rows (PL IV. Fig. 1 ; PL VII. Fig. 8) ; they are particularly powerful round 

 the opening of the mouth. 



The rejection of the digested food takes place quietly, and there are none of 

 those violent jerks attending its admission into the digestive cavity. The anal 

 opening simply expands, and the fecal matter is forced out slowly, in a constant 

 stream, until the whole of the contents of the alimentary canal, which had become 

 very much distended before the operation, has been cleaned > out. 



Motion and Habits of the Larvw. — The adult larva? move about rapidly by means 

 of the cilia; their natural position is more constant than when young. The oral 

 extremity is kept in advance while in motion, and the larva still rotates about a 

 longitudinal axis, though not frequently ; it generally moves with either the dorsal 

 or ventral side uppermost, and quite frequently in such a way as to show the lateral 

 groove. 1 When at rest, the larvas invariably assume one and the same position ; the 



1 The position in which the larvae figured in this stages, it is necessary to have them all in the same 

 memoir have been placed, requires a short explana- position, and this should, if possible, be the natural 

 tion. To be able to compare readily the different attitude. But, in the younger stages of the larva, 



