41 



monest miinhcr : on the edge and also on the upper surface of the flattened 

 branches, thoy occur singly or in small groui)s ; they are placed on a short stalk, 

 the longest measuring fully 1 mm., at an angle which varies from acute to right 

 but is usually right. Young 

 p()ly])s with practically no stalk 

 arise at the base of and in the 

 angles between the polyp- 

 stalks. The heads are small, 

 the larger measuring on an 

 average 0*6 mm. x 06 mm. ; 

 others are only 045 mm. high 

 and 066 mm. broad. The 

 spicules are arranged in eight 

 double rows of five to seven, 

 but usually of six pairs each ; 

 of each ujjpermost pair one may 

 project for a very short dis- 

 tance. This may be seen more 

 markedly in the lateral rows 

 of the smaller polyps (the small- 

 ness of which may be due to 

 their being greatly retracted). 



There are two rows of spicules on the aboral surface of the tentacles. The 

 polyp-spicules are Hat spindles either straight or curved, with a few simple 

 thorns ; they measure on an average 0"24 mm. in length, while the larger 

 spicules reach a length of 0:36 mm. 



The Stiitzbiindel is well developed, consisting of five to six spicules which 

 form a sheath for the back of the polyp-stalk and measure up to 3 6 mm. in 

 length. One always projects for a considerable distance, about 105 mm., 

 beyond the polyp, and a second projects for a very short distance in almost 

 every case. The various stages of development of the Stiitzbundel can be well 

 studied in this specimen — small spicules of equal size ; others similar, but more 

 closely arranged ; slightly larger spicules which scarcely project ; and the com- 

 plete form. 



Cortical spicules : (a) The stem has slender spindles, straight or curved, 

 with few small si)ines, and measuring from 048 to 3-75 mm. in length, and 

 from 0-03 to 01 5 mm. in breadth. On the main stem and branches they are 

 loosely arranged, at one part more transversely, at another more longitudinally, 

 but always tending to become more regularly longitudinal towards the base of 

 the smaller branches, on which they are more or less longitudinal in position. 



(b) Those of the stalk include slender spindles similar to those of the 



Fig. 23. D. masoni. 



