MUSEUM OF COMPARATIVE ZOOLOGY. 55 



Fig. 4. An older starfish, seen from the actinal side, showing the arrangement 

 of the plates. The soft parts in this and the former figure have heen removed. 

 Spines are removed from most of the terminals, and appear on one arm only. 



PLATE III. 



Fig. 1. Single arm of a starfish somewhat older than PI. II. Fig. 4. View from 

 the actinal side. Three ambulacral rafters have appeared. The youngest, am-, is 

 very small. 



Fig. 2. Somewhat older starfish, in which four ambulacral rafters have formed, 

 and in which the interambulacrals have begun to develop. View of one arm 

 from the actinal region. The specimen is slightly older than PI. III. Fig. 1. 



Fig. 3. View of the tip of the arm of a somewhat older starfish, showing the 

 terminals and the ambulacrals just forming under the protection of the terminal. 

 The ends of the spines are not represented. 



Fig. 4. View of the arm and the plates of the body of a somewhat older star- 

 fish than Fig. 2. Seen from the actinal side. The outlines only of the plates of 

 the body are represented. 



PLATE IV. 



Fig. 1. Abactinal view of an arm of a starfish a little older than PI. III. Fig. 1, 

 •showing dorsocentral, two genitals, the first of the medial dorsal line of plates, 

 and the terminal with its spines. Ambulacral plates in this and in Fig. 2 shown 

 through the abactinal system. 



Fig. 2. Abactinal view of an arm of a starfish older than Fig. 1. Portions of 

 two genitals, the marginals, dorsals, and a terminal, are represented. 



Fig. 3. View of a starfish from the abactinal region. From a specimen some- 

 what older than that shown in Fig. 2. Four of the arms have the plates shown 

 in outline only. The plates of a single arm are shaded, and the spines are 

 represented. 



Fig. 4. View of a single arm and the plates of the body of a starfish much 

 older than the last. Seen from the abactinal side. Soft parts have been removed. 

 Spines not represented on genitals and first dorsals. 



PLATE V. 



Fig. 1. View of the genital and first dorsal (radial) plates of the body of a 

 young starfish, of about the same age as PI. IV. Fig. 1. All the plates of the arms 

 removed. 



Fig. 2. The same somewhat older, showing the first formation of the plates, 

 dd l , between the ring of genitals and the dorsocentral. 



• Fig. 3. Still older starfish, showing the body plates between the ring of geni- 

 tals and the dorsocentral. View from the abactinal region. The radial lines are 

 from d l to dc. 



Fig. 4. Much older starfish, showing the network of plates which compose the 

 abactinal surface of the body. These plates are from a starfish almost an inch in 

 diameter (from tip of one arm to another). 



