182 
_ 
wide, and *75 mm. high (7.e., antero-posterior diameter). The 
proportions vary considerably, however, some shields being 
higher and narrower than the average, others being shorter 
and wider. The measurements above stated were arrived at 
by striking the average of the measurements of twenty-four 
well-expanded shields removed from the polypides and mounted 
in glycerine for microscopic examination. 

TeExt-Fic. 1. Buccal shields of Cephalodiscus gilchristi in various stages 
of development. A,—the shield of a young bud. B,—shield of an older bud. 
C,—shield of an older bud than the last ; no plume-rudiments were recognis- 
able in this bud. D,—shield of an older bud than the last ; the first two pairs 
of plumes of this bud were recognisable as hemispherical knobs ; the red line 
of the shield has now appeared. E,—shield of a fairly old bud; the first 
three pairs of plumes of this bud were clavate and devoid of pinnules, the 
fourth pair were hemispherical knobs. F,—shield of an adult polypide.'g All 
the figures are drawn to the same scale, namely, X 60. 
