MOTION AND HABITS OF THE LAEVJ5. 27 



of the oesophagus is covered with vibratile cilia, so closely crowded that 

 the walls appear striated from the regularity of these rows (PI. IV. Fig. 1 ; 

 PI. 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 Larvce. — The adult larvfe 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 Avay as to show the lateral groove.* When 

 at rest, the larvae invariably assume one and the same position ; the 

 anal extremity is the lowest, and the oral extremity inclined to the ver- 

 tical ; in this attitude they often remain a long time, drifting about with 

 the currents ; their only movements being the expansion and contraction 

 of the oesophagus and the play of the arms. The movements of the 

 arms are exceedingly graceful ; comparatively longer and more slender 

 than the tentacles of the Tubularians, they have none of the stiffness of 

 their movements, the constant curving and thrusting in every direction 



* The position in which the larvse figured in this memoir have been placed requu-es a short ex- 

 planation. To be able to compare readily the different stages, it is necessary to have them all in 

 the same position, and this should, if possible, be the natural attitude. But in the younger stages 

 of the larva the body of the embryo is not loaded down at one extremity by the young Starfish, 

 thus compelling the larva to assume always one and the same general attitude when in motion. It is 

 more common, in the younger stages, to see the embryo moving with the anal extremity uppermost ; 

 it would be as unnatural to turn these younger stages upside down, as it would be to represent an 

 adult larva in anything but its natural attitude (PI. VII. Fig. 8) with the anal extremity downward. 

 I have therefore compromised, by representing all the stages in the same position in which they are 

 generally represented by Miiller, to facilitate the comparison with his figures, and have given one 

 figure of an adult Brachiolaria, in its natural attitude (PI. VII. Fig. 8), with which the others can be 

 readily compared in their theoretical position. The figures here given are drawn from the larvte as 

 they appear swimming through the water; and I have endeavored, as much as possible, in repre- 

 senting them, to give an accurate idea of the mobility of the arms ; avoiding, in this way, the un- 

 natural stiffness which characterizes drawings made under compression, like the majority of those of 

 Miiller. 



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