GEROULD: CAUDINA. 
17 
the transverse musculature, fibers of which may have grown out 
through the connective tissue of the integument and sooner or later 
acquired the arrangement suggestive of that of the muscle fibers of 
the ambulacral vessels. I cannot imagine, however, in that case 
what could have been the cause of the arrangement of the fibers 
into a hollow cylinder. The uniformity in the occurrence of this 
arrangement into cylinders inclines me, therefore, in the absence of 
any embryological evidence, toward the former view. 
Whatever may be the morphological significance of these muscular 
cylinders, their present function seems to be to support the transverse 
muscles by providing for them an insertion in the firm outer part 
of the integument which contains the calcareous bodies, and further- 
more to unite firmly together the various parts of the integument. 
Semper (’68, p. 46) undoubtedly had these structures in mind in 
describing rudimentary ambulacra in Haplodactyla molpadioides 
and Caudina arenata. These forms, he says, “besitzen sowohl die 
Radiarcanale wie auch die von ihnen ausgehenden, quer die Haut 
durchsetzenden Wassergefasse, welche bei den fiissigen Ilolothurien 
in die Fusschen ubergehen, hier aber unter der Epidermis blind 
endigen.” Teuscher (’76, p. 549), on the other hand, positively 
denies the existence in Caudina of any such lateral branches of the 
radial canal as Semper describes. Danielssen and Koren (’82) 
state that in Trochostoma. Thomsonii the radial canals along their 
course send numerous lateral branches which end blindly in the 
skin, and Sluiter (’81) makes a similar statement in regard to 
Haplodactyla hyaloides. I have found no muscular tubules in 
preparations of the integument of either Trochostoma antarcticum 
or Ankyroderma Jeffreysii. 
3. CALCAREOUS BODIES. 
The calcareous bodies in the integument of Caudina (Plate 3 , 
figs. 17-19, 26-33) are similar in form to the stool- or table¬ 
shaped spicules of the Cucumariidae and Holothuriidae; the leg of the 
table always points outward, i. e., away from the axis of the body. 
A complete calcareous table is composed of a smooth, flat, nearly 
circular or oval disc, measuring in an average of twenty speci¬ 
mens 106.6 ix broad by 116.9 /x long. The disc of the smallest 
table measured was nearly circular and 91.5 fx in diameter, 
whereas that of the largest one was 132 fx by 135 fx in dimensions. 
