100 STUDIES IN GENEKAL PHYSIOLOGY 



end, as illustrated in Fig. 11. In this experiment I had cut 

 a long broad piece aa l out of the tube at a, so that the 

 anterior piece of the tube a t & 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 Serpulidse, however, the calcareous tubes of which are 

 stiff and inflexible. These Serpulida3, like Spirographis, 

 expose their gills to the light, and these, too, react according 



