62 
CAULOPHACUS SCHULZEI. 
the number, position, arrangement, and shape of the latter are not the same 
in the large and small discocomes. To obtain an insight into the correlation of 
the various peculiarities of the discocomes of different size, I measured thirty- 
three of these spicules all from the same large specimen (E). The smallest of 
which all the dimensions were taken was 70 n in diameter, the largest 312. 
Discocomes less than 70 n in diameter are rare, the smallest observed was 44 n, 
and these small ones are probably only young forms. As I was unable to take 
with sufficient exactitude all the measurements required of these small disco- 
comes I have not taken them into consideration in the correlations of the several 
characteristics. The difference of the diameters of the smallest (70 n) and the 
largest (312 /*) completely measured discocome is 242 ju. This 242 m represents 
the range of variation in size (diameter) of the thirty-three discocomes studied. 
The fourth part of it was taken, 242 : 4 = 60.5, and thus the variation-range 
itself divided into four equal parts, each extending over 60.5 n of diameter- 
variation. To the first of these four parts belong all the discocomes 70-130.5 n 
in diameter, to the second all 130.5-191 n, to the third all 191-251.5 n, and to 
the fourth all 251.5-312 /z. The discocomes belonging to the same quarter of 
the diameter-variation range were considered as forming a group and their meas- 
urements combined. The subjoined table (p. 63), gives the measurements of 
the four groups of differently sized discocomes. 
The table indicates that the small discocomes (of group I) are more numer- 
ous than the larger, and that among the latter those of group III (191-251.5 n 
in diameter) are scarcer than those of groups II and IV. It further shows that 
the relative length of the main-rays is in inverse proportion and the relative 
length of the end-rays is in true proportion (total diameter) of the spicule, that 
is, the larger the discocome the relatively longer the main-rays and the relatively 
shorter the end-rays. 
The number of end-rays on each main-ray and the degree of their divergence 
(the width of the apical angle of the bunch or verticil formed by them) are in 
inverse proportion to the size of the spicule; largest in the smallest (group I) 
and smallest in the largest (group IV). Besides these differences of the relative 
dimensions of the parts of larger and smaller discocomes, also differences in 
the shape and arrangement of the end-rays are to be noticed. In the small 
discocomes (Plate 10, figs. 17, 18, 24, 25) the end-rays are more or less curved 
in an S-shaped manner, in the large discocomes (Plate 10, figs. 19-21) they are 
straight. In the small discocomes, where they are more numerous, the end-rays 
form bru.sh-like bunches, whilst in the large discocomes, where they are fewer 
in number, they are arranged in a simple verticil. The terminal thickening of 
