100 SruDIES IN GENERAL PHYSIOLOGY 
end, as illustrated in Fig. 11. In this experiment I had cut 
a long broad piece aa, out of the tube at a, so that the 
anterior piece of the tube a,b remained attached to the rest of 
the tube only by a thin piece p. After the operation the 
animal showed its gills at a, and no longer used the piece a,b 
of the tube. New material was deposited at a within a few 
days, and in the course of three weeks the new piece ac was 
formed. Its light color readily characterized it as new. 
I had at the same time cut away the aboral end of the 
tube completely. Before my very eyes the movement of the 
aboral end upon the sand caused the secretion of a sticky 
mass, to which particles of sand became attached. In this 
manner the new piece of tube de was built, consisting of 
grains of sand cemented together by the glandular secretion 
from the tube. The newly formed piece was perfectly 
smooth on the inside. The secretion from the skin glands 
continues as long as there is any noticeable amount of fric- 
tion. When I removed Spirographis from its tube and 
placed it in a smooth test-tube, practically no secretion 
occurred. Secretion occurred only from the parapodia in 
the form of long, fine threads, similar to those produced by 
the spinning glands of spiders. If, however, the naked 
Spirographis was laid upon the sand, the aboral end was 
soon covered by a shell of sand kernels. I have never, 
however, seen the animals form a complete tube when 
removed from their old ones ; for in their exposed condition 
they soon die. 
II 
Spirographis Spallanzanii attains its heliotropic orienta- 
tion when illuminated from one side by curving its flexible 
tube; new growth of the tube is not necessary. There are 
other Serpulide, however, the calcareous tubes of which are 
stiff and inflexible. These Serpulide, like Spirographis, 
expose their gills to the light, and these, too, react according 
Digitized by Microsoft® 
