Tube sea squirt, Ciona mtestinalis, 5 inches high, fil- 

 ters food out of the water that is drawn into the open- 

 ing on the left and discharged through the temporar- 

 ily closed one on the right. ( England. D. P. Wilson ) 



has been removed. Each individual of the colony 

 takes water and food particles through incurrent 

 openings on the outside of the colony, and discharges 

 the water again from atrial openings into the central 



cavity. The combined flow is enough to propel the 

 colony endwise — jet propulsion of the mildest kind. 



Pyrosomes found near the surf or netted from the 

 sea usually fall in the size range from 1 to 5 inches 

 long and from % to % of an inch in diameter. Oc- 

 casionally a really large one is collected at night, 

 when the display of its luminescence is so vivid. One 

 pyrosome colony 4 feet long and 8 inches in diame- 

 ter was brought up and handled by scientists and 

 crew aboard an oceanographic research vessel. Be- 

 fore preserving their trophy, the men amused them- 

 selves for half an hour by writing their names in 

 light on its surface — merely by tracing a finger tip 

 gently over the outer ends of the small animals that 

 composed it. 



None of the other thaliaceans is colonial. They 

 are known as salps, and they combine a barrel- 

 shaped body with extreme transparency. Many of 

 them are evident in the water only as a regular 

 series of hoopHke muscle bands, seemingly with no 

 connection. Slow pulsations of these muscles drive 

 water in through the mouth opening at one end, 

 through the huge pharyngeal sieve, and out of the 

 atrial opening at the other end. 



One crustacean of almost equal transparency 

 (Phroiiinui) is sometimes found riding along in this 

 transparent-walled cavity. Nearly always it turns 

 out to be a female feeding on larger food particles 

 swept in by the salp, and using the pharyngeal bas- 

 ket as a convenient place in which to raise her young. 



Salps reproduce both sexually and by budding. 

 Often the buds develop into fully grown individuals 

 while still attached to the parent. In this way, long, 

 delicate trains of salps arise. In Doliohim the budded 

 individuals migrate over the surface of the parent and 

 attach themselves temporarily to a dorsal projection, 

 taking places in three rows of remarkable regularity. 



The Laiicelets 



(Suhphyluni Cephalochordata) 



Along sandy coasts of most oceans where the wa- 

 ter is as warm as in North Carolina, southern Eng- 

 land, the Mediterranean, or Japan, if a shovel is 

 thrust suddenly into the wet beach at the low-tide 

 line and the handle pulled back sharply, little trans- 

 lucent flesh-colored animals may jump out and bury 

 themselves rapidly close by. If a person is quick, a 

 few can be captured. Each turns out to have a flat- 

 tened slender body pointed at both ends, but no 

 paired appendages or very obvious tins. It is a lance- 

 let, a link between the vertebrates and the more 

 widely known kinds of invertebrates. 



Through sand that is very wet or under water, 

 lancelets can swim almost as easily as a minnow in 



288 



