CALYCOSILVA CANTHARELLUS. 
79 
larger, there is no room on the ray for the development of a spineless distal part, 
and there is not even on the whole ray space sufficient for the spines to be placed 
at so great a distance from each other as in the spined regions of the normally 
developed long ones. It seems very probable that this crowding may lead to a 
partial concrescence of two or more adjacent spines and thus to the formation 
of the apparently branched structures above referred to, which I am inclined to 
consider as more or less coalesced groups of as many spines as they bear terminal 
spinelets. 
Of hexactine-derivates with less than six rays pentactine, tetractine, and tri- 
actine forms have been observed in all varieties, diactine ones, however, only 
in C. c. var. simplex. Several pentactine to triactine forms have been observed, 
in C. c. var. megonychia. In the two other varieties they are exceedingly rare. 
Apart from the smaller number of their rays, they do not differ from the hexac- 
tines above described. The diactine forms are much more frequent than those 
in C. c. var. simplex. 
The diactine hexactine-derivates (Plate 1, figs. 25-29; Plate 2, fig. 5), which 
I have found only in C. c. var. simplex, appear as straight, or slightly curved, or 
angularly bent, blunt, usually isoactine amphioxes. They are 2. 6-3. 3 mm. 
long and 40-90 n thick in the middle, where a slight thickening is sometimes dis- 
cernible. Some taper from here uniformly towards both ends, in others each 
actine is thickened some distance from the centre. The transverse diameter 
» of these thickened parts is in such spicules 10-15 fi greater than that of the centre. 
These hexactine-derivate amphioxes bear spines, the size, number, and arrange- 
ment of which are subject to considerable variation. A part of the spicule, situ- 
ated at or near the middle of its length, is always free from spines (Plate 1, figs. 
25-29). Farther on the two actines bear spines, which are either sparsely and 
irregularly scattered (Plate 1, figs. 25-27) or restricted to distinct belts, one on 
each actine, within which the spines stand rather close together (Plate 1, figs. 28, 
29; Plate 2, fig. 5). In shape and size the spines of these amphioxes resemble the 
spines of the hexactines above described. A few of the spines are branched 
(bifurcate). 
The pentactines have very much the same shape and size in the three varie- 
ties, and there seems to be hardly any difference between the hypodermal and 
the hypogastral pentactines of the body. The pentactines of the stalk are 
smaller and have a relatively shorter apical (proximal) ray. 
The four lateral rays of the hypodermal (Plate 6, figs. 1-8) and hypogastral 
(Plate 1, figs. 5-13) pentactines of the body proper are 250-770 n long, usually 
