28 EMBRYOLOGY OF THE STARFISH. 



reminding us rather of the motions of the tentacles of Phyllodoce and 

 similar Annelids. They are never at rest, being always kept in motion 

 to produce currents round the mouth of the larvae ; and, in addition to 

 the action of the powerful vibratile cilia placed round the mouth, are 

 continually bringing fresh water into the oesophagus. 



The large triangular mouth (PI. IV. Fir/s. 1, 2, 4, m ■ PI. VII. Fig. 8) 

 opens into a rectangular pouch (PL IV. Fig. 4, m', m"), extending back 

 from its posterior edge ; from this pouch the oesophagus tapers rapidly, 

 and attains, near the apex of the mouth, the size (o) which it retains till 

 it joins the stomach. The surface of the oesophagus (o) presents a more 

 or less corrugated appearance near its junction with the digestive cavity, 

 owing to the somewhat greater thickness of the walls (PI. IV. Fig. 1). 



Brachiolar Arms. — The brachiolar arms (//,/") are appendages belong- 

 ing only to adult larvae. Our larva has three of them (PI. IV. Figs. 1, 4, 

 5, 6), one pair (//), and a somewhat larger odd arm (/"), placed at the 

 base of the odd anterior arm (e") ; the branches of the water-system ter- 

 minating in these arms proceed from a large pouch {wiv) in the oral ex- 

 tremity (PI. IV. Fig. 4). The brachiolar arms are, like the others, tipped 

 with orange, but have, in addition, wart-like terminal appendages, each 

 having six to eight nipples, according to the age of the larva (PI. IV. 

 Figs. 4, 5, 6, 8; PI. VII. Fig. 8). These knobs give to the short arms 

 the appearance of the hind feet of Sphinx larva?. In the hollow between 

 the base of the brachiolar arms there is a small elliptical disk (/'", PL 

 IV. Figs. 4, 5, 6 ; PL VII. Fig. 8), reminding us of the madreporic body 

 of a Starfish, nnd a row of similar disks, two or three on each side of the 

 odd 'brachiolar arm, the pair of small brachiolar arms having no such ap- 

 pendages. It has been found convenient to retain for these peculiar arms 

 tlie name of brachiolar, used by Miillcr to distinguish one of his genera 

 (Brachiolaria) of Echinoderm larvae. I have not succeeded in ascertain- 

 ing the functions of the disks ; the terminal buttons undoubtedly are used 

 in the last stages of g»'owth of the larva as supports, by means of which 

 they can attach themselves, while tlie young Starfish is resorbing the 

 larva; for during that process the larvae never float about, but invari- 

 ably sink to the bottom of tiie jar in which they are kept, and remain 

 attached, apparently by means of the brachiolar arms, during the resorp- 

 tion of the larval appendages. 



These larva^ are found lloatinsj^ in large numbers at nii'ht near the 



