SqUIMTS, POLYPS, AND JELLY-FISHES. 



55 



adhering to the piles. Press gently with the finger — 

 the animal contracts, and while contracting throws 

 out a double jet of water from two chimney-pot open- 

 ings situated on its surface. The animal is one of our 

 commoner forms of sea-squirts, known to naturalists 

 as Molgida Manhattensis. Through its pel- 

 lucid outer tunic the color of the viscera 

 can be indistinctly seen. This species 

 also frequently attaches itself to floating 

 sea-weed, and is then drifted in to shore ; 

 or it may be found attached to the nod- 

 ding fronds which battle with the waves. 



The sea-squirts are in many ways interesting 

 animals, especially since it has been shown that in 

 their young condition they present many points 

 of resemblance to the vertebrate or backboned 

 animals. Thus, the larva of most species has a long 

 tail, a rudimentary spinal column, and a long nerve- 

 tract, terminating in a brain, which occupies the 

 same relative position to the spinal column that the 

 same tract does in the higher animals. Indeed, so 

 similar is the larva of 

 certain forms to a tadpole 

 as to carry with it a con- 

 viction that the two can- 

 not be very far removed 

 from each other. But in the mature form of 

 nearly all squirts the tail becomes absorbed, and 

 with it disappears what there was to represent the 

 spinal column, and also much of the nerve appa- 

 ratus — a case of true degeneration. One of the 

 chimney pot openings on Molgula conducts into 



Labva op tunicate. 



