TUBICOLAR ANNELIDA. 15 



the apex is much thickened, the initial point having been removed or absorbed; 

 the annulations are obsolete and the surface lamellose. The specimen is 

 attached for the greater part of its length to the calyx of an Eucalyptocrinus 

 crassus. Figure In represents the largest specimen observed. The apex and 

 the surface of adherence have been broken off, and only the free portion re- 

 mains. This preserves the concentric lamellose-annulate character, and finely 

 striated surface. 



Figures 11 and 12 are interesting as showing an irregular lamellose growth, and 

 the fracturing of the test, which has been subsequently healed duringthelife of the 

 animal. In many instances, where the test has been broken and again restored, 

 the continuity of the strife is interrupted, as illustrated in the specimen, fig. 13. 



As the individuals advance in growth, the inner and outer walls of the 

 tube become separated, and the intermural space filled with vesicular tissue. 



This separation of the walls and the development of the tissue is not always 

 in proportion to the size of the individual, nor is it uniform on all parts of the 

 circumference of the tube in the same specimen. It is rare that individual tubes, 

 cut longitudinally through the center, show an equal development of this tissue 

 on the two sides. In figure 14, a section of a small individual, the tissue on one 

 side encroaches largely upon the visceral cavity, while on the other it is only 

 incipiently developed. Figure 15 shows an unequal development of the tissue 

 on the two sides; and figure 1G, a section of one of the largest individuals 

 known, shows but an incipient development of this tissue. 



In figure 17 this vesicular structure is subequal on the two sides, while fig- 

 ure 18, a farther enlargement, shows the vesicles developed within the inner 

 walls and encroaching upon the visceral cavity. This irregularity is especially 

 shown in the transverse section, figure 19, where upon two sides there is no 

 development of tissue, the walls being apparently quite solid as represented. In 

 figure 20, however, we have a more distinct manifestation of this unequal de- 

 velopment, where the upper or barren side, as shown in the figure, has probably 

 been the attached surface. While there is a general similarity in this vesicular 

 texture, there is no uniformity in size or form of the vesicles, as may be seen in 

 any one of the sections, and especially in figures 18 and 21 of plate cxvi. 



