FOUND LINKS. 



145 



we find the Tunicate*, Ascidians, or " Sea Squirts " 



(Fig. 11), to present us with certain highly interesting 



features for remark. These ani- 



mals are usually regarded as poor 



relations of the shell-fish or Mol- 



luscs ; and they exist both in a 



fixed and free state. The fixed 



sea squirts are tolerably common, 



and are found attached to shells 



and other objects dredged from 



deep water. Each sea squirt is 



a clear leathery bag, an inch or 



two in length. Like the old f ' wine- 



skin" it has two necks or openings 



(d, i). One leads into a white 



throat or pharynx (A), the walls 



of which are richly ciliated, and 



which are perforated by numerous 



openings, whilst the whole throat, 



like that of the lancelet, is richly 



supplied with blood-vessels. The 



other opening is a door of exit. 



It leads from a sac or bag, called 



the atrium, into which the water 



used in breathing is wafted from 



, T , i mi i 



the throat. Ihus, when a sea 



squirt breathes, the water is in- 

 , . , , ,, . 



haled by the mouth - opening, 



aerates the blood contained in the vessels of the 

 throat, and is then sent into the atrium, whence 



L 



^ u __ Amm , rouci . 

 ^^> a Sea Squirt. 



( A J Pharynx, or respira- 

 tory portion of the 

 bod F; B > stomach; c, 

 egg-producing organ.) 



