DESCRIPTION OF THE PLATES. 



Plates I.-YI. illustrate the spicules of Holothurians, magnified, 

 unless otherwise stated, 290 times. Spicules for microscopic 

 observation can he readily prepared by cutting off a podion or a 

 small portion of the skin, and treating it with a few drops of 

 caustic potash at a moderate heat. 



Plate I. 



Pig. 1. Anchors and plates of Synapta inlicerens (p. 33). 

 Pig. 2. „ „ „ buslci (p. 34). 



Pig. 3. ,, ,, „ digitata (p. 34). 



Plate II. 



Fig. 1. a, Plates from the body- wall ; and b, Spicules from the 



podia of Cucumaria hyndmani (p. 36). 

 Fig. 2. The same from Cucumaria planci ; c, Spicules, x 450 



(p. 37). 



Plate III. 



Fig. 1. a, Plates from the body-wall ; and b, Spicules from the 



podia of Cucumaria pentactes (p. 37). 

 Fig. 2. The same from Cucumaria lactea (p. 38). 



Plate IV. 



Fig. 1. Spicules of Cucumaria hispida, shown as large as they are 

 for the purpose of being easily compared with the 

 others, as they are drawn to exactly the same scale as 

 most (p. 38). 



Fig. 2. The same of C. frondosa ; these generally become less nume- 

 rous as the animal increases in size (p. 39). 



