168 SEA-SHORE LIFE 
The minute animal and vegetable organisms that are drawn 
in with the water do not pass through the gill slits, but are caught 
in the slime that lines the throat and passed around, entangled in a 
cord of slime, into the stomach. 
The heart is a spindle-shaped tube lying under and near the 
stomach. Curiously enough it pumps blood in one direction for a 
few moments, then rests, and pumps in the opposite direction. 
The blood corpuscles are 
mainly colorless and con- 
stantly change their shape re- 
sembling amoebe. Some of 
the blood corpuscles are, how- 
ever, of definite shape and are 
often deeply colored, being 
reddish, indigo, brown or 
even white. It has been found 
that when bacteria or other 
disease germs are introduced 
into the blood system, the 
colorless blood corpuscles 
seize upon them, and attempt 
to engulf them. Sometimes, 
however, they do not succeed 
but are themselves destroyed 
in the attempt to digest the 
bacteria, and then tlie disease 
conquers in the strife. 

Fig. 118; CIONA INTESTINALIS. From The genital eee cia 
Woods Holl, Mass. found close to the side of a 
loop of the intestine, and their 
duct opens at the dorsal spout. In common with many sedentary 
and degenerate animals all tunicates are hermaphrodites, but the 
same individual does not usually fertilize its own eggs. 
The ‘“‘brain” or principal ganglion of the Tunicate is situated 
midway between the two spouts, and is simply the remnant of the 
larval brain. It is, however, of so little importance that if it be 
cut out the creature lives quite well, and is even capable of contract- 
ing in a normal manner when touched. The “brainless” animal 
