52 L. HrLLIS-COLINVAUX 



platform-like edge of the utricle (Hillis, 1959), so that these utricles 

 may separate readily after decalcification if the coverslip over the 

 preparation is pressed gently. 



The degree of adhesion also varies somewhat with the age of the 

 segment. In some species at least, the utricles, while adhering in young 

 and mature segments, may separate readily in old yellowish or whitish 

 basal segments (Hillis, 1959), and sometimes in mature segments as 

 well (Fig. 17). 



(v) Number of peripheral utricles supported by a secondary utricle. 

 Longitudinal sections (Subsection 2.b.iii) are required to observe this 

 character, and some of the range is illustrated in Fig. 20. 



Usually 2 or 4 peripheral utricles are supported by each secondary 

 utricle. In favulosa, however, sometimes only one is borne on a 

 secondary utricle, in bikinensis and gracilis up to 8 frequently may be 

 so supported, with as many as 14 in discoidea and 18 in lacrimosa. 

 Numbers between 2 and 8 occasionally occur in species in which 2 or 4 

 are usual (Hillis, 1959). 



(e) Shape, diameter and length of inner utricles. Inner utricles show up 

 in longitudinal sections like those described in Subsection 2.b.iii. They 

 are best seen at x 100 magnification when they appear rather like 

 expanded sacs, or sometimes as continuations of filaments, between the 

 outermost (primary) utricles and the longitudinally oriented medullary 

 filaments. Striking differences in shape and diameter are apparent in 

 different species, and length may also be a useful parameter. High- 

 power magnification ( x 400) should be used in measuring the diameters 

 of the inner utricles at the small end of the size range. Utricle diameter 

 is measured at what is usually the broadest part, just below the 

 insertion of the primary utricles. 



The most dramatic secondary utricles are the greatly swollen 

 "bullate" utricles of the Atlantic discoidea (Fig. 20, No. 11), and in 

 these plants usually only two layers of utricles, the peripheral and 

 secondary, are present. In Pacific-Mexican and Hawaiian discoidea, a 

 third or tertiary layer of utricles is commonly present and then the 

 secondary utricles are less conspicuous and at the lower end of the size 

 range (Howe, 1911; Hillis, 1959). 



Other distinctive secondary utricles are those of lacrimosa, and to a 

 lesser extent gracilis (Fig. 20, Nos. 12 and 9, respectively). Those of 

 lacrimosa are frequently very long and are much swollen at their 

 peripheral end. Those of gracilis are of a similar style, long and swollen, 

 but the amount of distension at the peripheral end is considerably less 

 and sometimes almost imperceptible (Hillis, 1959, and Section IV). 



