NO. 1658. ALCYOJSIARIA OF THE CALIFORNIAN COAST— NUTTING. 695 



THE ZOOIDS. 



The two zooid bands extend the whole length of the rachis, being 

 over 7 inches long and 0.6 broad at the widest part, narrowing 

 gradually distally, and ending each in a somewhat curved lobe 

 proximally. The mass is swollen and turgid to within about J 

 inch of the proximal end, where it is suddenly contracted, the remain- 

 der being on a lower level, as seen from the ventral aspect. This 

 proximal area on each band seems to be occupied by undeveloped 

 zooids, as they are much smaller and less prominent than elsewhere. 



The bare streak between the lateral bands of zooids is about half 

 an inch broad at its widest part basally, and becomes almost oblit- 

 erated distally. Its width and also the extent to which it is depressed 

 between the lateral bands depends largely on the extent to which 

 the rachis is injflated and the method of preparation of the specimen. 



Both edges of the lateral bands are perfectly even, straight, and 

 clearly defined. The bands do not reach the leaf bases laterally by 

 about 0.16 of an inch. 



The zooids are densely crowded together over the whole surface of 

 the bands, and are greatly distorted by mutual pressure, so that their 

 real shape is hard to ascertain, their outUne being as varied as so 

 many cobblestones in a pavement. (Fig. 10, Plate LXXXV.) 



In general they present the appearance of conical or dome-shaped 

 papillae, inclined somewhat toward the distal end of the colony and 

 surrounded or partly surrounded by spicules. A terminal mouth is 

 present, but closed so tightly that nothing but a sHght depression can 

 be seen. There are no true tentacles, although a scalloped appear- 

 ance around the periphery of the zooid might suggest them. 



Many minute zooids are crowded between the larger ones, as if 

 there were a succession of these structures in various stages of growth ; 

 moreover, there are many deep infoldings and convolutions of the 

 surface which bears the zooids, so that many of the latter are carried 

 some distance below the surface, as is shown by transverse sections 

 of the zooid bands. Such a section, taken across the racliis, shows 

 that the zooids are simple, sac-like bodies with an elongated oval 

 body cavity, the upper portion of the walls being beset with numer- 

 ous spicules. The lower end of the body cavity is continued broadly 

 into a canal which passes downward and opens into one of the numer- 

 ous canals that are longitudinal to the rachis and form a series the 

 openings of which, in such a section, are regularly disposed a short 

 distance beneath the zooids. Below this zone of longitudinal canals 

 are seen transverse sections of numerous complicated muscle bands 

 which, like the canals, are disposed in a regular zone or layer running 

 lengthwise of the rachis. 



These muscle bands are the most striking feature of the section, 

 and indicate the most powerful and highly specialized muscles of the 



