60 



Arenicolidae 



and these are subdivided into only two to four gill-filaments. These 

 gills have therefore a bushy appearance. 



The gills of A. assimilis and of the examples of the var. affinis 

 from Auckland Island are similar to those of the littoral form of 

 A. marina, from which they differ only in the absence of " webbing " 

 at the base of the gill-axes. The gill-filaments of most of the 

 specimens examined are elongate, almost as long relatively as those 

 shown in Fig. 31. Examples of A. assimilis var. affinis from New 

 Zealand, the Falkland Islands and South Africa have pinnate gills. 



A. glacialis has small gills, which present an extreme form of the 

 bushy type. The axes even of the largest gills are not more than 2 mm. 

 long. The most fully expanded gill found on any of the specimens 

 is shown in Fig. 33. It consists of nine or ten axes, which arise from 

 a short, curved, common basal structure situated immediately behind 



Figs. 33, 34. — A. glacialis. Two gills from different specimens. A few gill-axes have been cut 

 away to affDrd a better view of the rest. 



the notopodium. The longest axis (c) bears five forked branches ; 

 of the resultant gill-filaments the longest are thumb or finger-shaped 

 and not more than •? mm. in length, and the shortest are mere 

 tubercles. The smaller axes of this gill bear only two or three 

 branches, which may be simple, that is, undivided distally (a, b). 

 A well expanded gill from another specimen is represented in Fig. 34. 

 It is smaller than that just described, the largest of the seven axes of 

 which it is composed being scarcely 1 mm. in length from its base to 

 the tip of its filaments. This axis (a) consists of three main stems, 

 each of which bifurcates, and one of the two so formed again divides, 

 but the other does not. In this manner, three groups, each of three 

 gill-filaments, are clustered at the end of the axis. In all the gills 

 examined the branches borne by an axis are clustered at tlie end, 

 the result of the great abbreviation of the axis. A. glacialis and 



