Iviii 
THE VOYAGE OF H.M.S. CHALLENGER. 
9, Amphitrisene (Fig. X., o). — Both actines of a rhabdome terminate in a cladome. 
The cladome of one end may be similar or dissimilar to that of the other (homopolar 
and heteropolar amphitriaenes). Thus the cladome at one end may be dichocladose, and 
at the other simply cladose. 
It will be observed that in the case of the trisene we have followed a different method 
to that we pursued in the case of the simple rhabdus ; since we have here retained the 
prefix “ amphi-,” and as a matter of fact left some such prefix as “.mono-” to be under- 
stood in the case of the other trisenes ; this is done as a matter of convenience, the 
monotrisenes being the prevalent forms, and the amphitrisenes of rare occurrence ; thus 
there is convenience in dispensing with the prefix “ mono-,” as its place can be better 
occupied. 
10. Centrotrisene (PI. XXXV. fig. 23).— The cladi arise from the centre of the rhab- 
dome, i.e., the actinal and cladal centres correspond. Though the cladi thus become 
geometrically actines, we shall continue to speak of them as cladi, since they are 
differentiated from those of the rhabdome as well as homologous with the cladi of 
other trisenes. 
In some cases the trisene is reduced by the loss of one or two of its cladi, it then 
becomes a disene or monsene as the case may be ; the varieties of these reduced forms are 
denoted like those of the trisene by the prefixes “ pro-,” “ ana-,” &c. 
We now pass on to the classification of the monaxon Monactine, or Style. 
Forms of the Style. 
1. Style {stilus, a style, Yosmaer) (Fig. X., g). 
When the single actine is strongylate at the origin and oxeate at the termination 
the term style is used without qualification. 
2. Tylostyle. — A style which is tylote at the origin Fig. X., h). 
Both the rhabdus and the style may differ in other respects as weU as in the 
character of the termination ; such differences are indicated by descriptive additions ; 
thus they may be fusiform, cylindrical, or nearly conical, or immeasurably thin 
(trichodal, hair-like), smooth or spined, and if spined partially or wholly. The 
spines also differ in character ; they may be large, small, erect or inclined, sharply 
pointed or rounded off, and so forth ; for very minute spines Carter uses the term 
“ microspines ” ; I have not felt at liberty to adopt this term, although it has the 
temptation of brevity, because it is a hybrid of Greek and Latin. 
