288 



LECTURE XIII. 



April, 1823, he captured, with a small muslin towing net, a number 

 of translucent animalcules, about the tenth of an inch in length, of a 

 subelliptic form, slightly compressed, and of a brownish tint ; the 

 body of each was defended by a shell composed of two valves, joined 

 by a hinge along the back, and opening along the opposite margin for 

 the protrusion of a large and strong anterior pair of limbs {fig.\2,Q, a), 

 126 provided with an adhesive sucker 



and hooks, and of six pairs of 

 posterior jointed members (6), 

 terminated by a pencil of bris- 

 tles. These natatory limbs acted 

 in concert, so as to cause the 

 animal to swim by a succession 



Pupal Balanus. ^^ ^^^^^^ jjj^^ ^j^^ ^^^^^ g^^^ 



(Daphnia). The body was terminated by a short tail (e), composed 

 of two setigerous joints. A pair of pedunculated compound eyes(rf) 

 was attached to the anterior and lateral part of the body. Other 

 specimens of this little seeming crustaceous animal were taken on the 

 1st of May, and preserved alive in a glass vessel of sea-water. On 

 the night of the eighth two of them had thrown off their outer skin, 

 and were firmly adhering to the bottom of the vessel, where they ra- 

 pidly assumed the form of the young of the sessile Barnacle called 

 Balanus pusillus. The sutures between the valves of the shell and of 



the operculum were visible, and 

 the arms, though not yet per- 

 fectly developed, were seen mov- 

 ing within. The eyes also were 

 still perceptible, although the 

 principal part of the black co- 

 louring matter appeared to have 

 been thrown off with the exu- 

 vium. On the 10th of May 

 another individual was seen in 

 the act of throwing off its exu- 

 vium, and attaching itself to the 

 bottom of the glass. As the cal- 

 cification of the shell proceeds, 

 the eyes gradually disappear, 



and the visual ray is extinguished 

 for the remainder of the animal's 

 life. The arms at the same time 

 acquire their usual ciliated 

 structure. 



127 



Larval Lcpat. 



