456 THE AQUARIAN NATURALIST. 



When the egg of one of these Compound Aseidians 

 is first hatched, the young progeny is seen to resemble 

 almost exactly a newly-born tadpole, which soon 

 extends its tail, and begins to swim about by the aid 

 of its undulatory movements. The tail is propor- 

 tionately large, and, like the body, is composed of 

 two distinct parts, the one superficial, colourless, and 

 of a gelatinous texture, the other central and yellow. 

 These larvse, after swimming about with an active 

 wriggling motion for a few hours, attach themselves 

 to the surface of some foreign object ; and if disturbed 

 from their position, set off and swim about as before, 

 until they meet with a suitable situation. Having 

 done so, their activity ceases, and they become per- 

 manently fixed, their size at this period being about 

 that of the head of a very small pin. They appear to 

 affix themselves to their resting-place by means of 

 some minute suckers situated upon their anterior 

 extremity. 



When once attached, the tadpole-like larva soon 

 loses all power of locomotion, and quickly undergoes 

 a strange kind of change in its configuration ; its body 

 becomes wide and sac-like ; its long tail, which pre- 

 viously played so important a part, is found entirely 

 reduced to its gelatinous or tegumentary portion ; and 

 speedily even this, becoming more and more trans- 

 parent, withers, and is finally detached, or falls away 

 in shreds, and totally disappears. These changes 

 ordinarily occur within the space of from ten to 

 twelve hours ; and if the larvse are examined towards 

 the close of the first few days of their sedentary ex- 

 istence, they will be seen to present the appearance 



