2942 



THE SEA SQUIRTS OR ASCI D I AN S 



gelatinous matter. After a brief free existence it fixes itself by its muzzle to some 

 submarine object, with the tail stretched out and generally motionless. In a short 

 time this appendage commences to shorten, and finally disappears, by being drawn 

 up into the body of the developing sea squirt and absorbed. A further process of 

 development results in the production of the perfect sea squirt; but it would be quite 

 foreign to the scope of this work to enter into the details of the metamorphosis; and 

 we may conclude this portion of our subject by stating that ascidians are probably 



PEAR-SHAPED ASCIDIAN, Hypobythius. 

 (One-twelfth natural size.) 



the degenerate descendants of permanently free-swimming forms provided with a 

 complete notochord and nerve tube; both of which structures are now in most cases 

 only temporarily retained in the tails of the larvae. 



According to the classification adopted by Professor Herdman, the tunicates may 

 be divided into three orders, the first of which is known as the Ascidiacea. This 

 group includes both fixed and pelagic, simple and compound types, none of which 

 are provided in the adult state with a tail and retain no trace of a notochord; the 



