MEM. M. C. Z., IX. No. 2. — ECHINODERMATA. 



25 



PLATE VIII. 



Development of Asteroidea, continued. 



Figures from Alexander Agassiz, Johannes Muller, 

 and S. Lov^N. 



a. 

 b. 

 c. 

 d. 

 d'. 



1. 

 V. 

 IK 

 m. 



V-- 

 1^ . 



2> c. 



Anus. 



Dorsal or water pore, madreporic opening. 



Alimentary canal. 



Digestive cavity. 



Abactinnl water-tubss in the angle of the rays 

 of the young Starfish. 



Eye of Starfish at the base of the odd tenta- 

 cle {/'). 



Dorsocentral plate. 



Interradial plate. 



bi-achial terminal plate. 



Mouth. 



Opening for passage of arabulacral sucker. 



(Esophagus. 



Spines on edge of ray of young Starfish. 



Spines of exterior rows along the abactinal 

 surface of the rays. 



Spines of middle row, on the abactinal .surf;ice 

 of the rays. 



Central spine of the abactinal surface of the 

 young Starfish, with centrodorsal plate (/). 

 . Different forms of pedieellarise. 



Plate at the junction of adjacent rays (ovarian 

 plate). 



Abactinal surface. 



?•'. First set of five limestone y rods which appear 

 on the abactinal surface, and eventually be- 

 come the terminal brachial plates (P). 



r". Second set of five y rods to appear on the 

 abactinal surface, ami which eventually be- 

 come tile iiitenadial plates (/'). 



»-'-c5. The first to fifth arm-lobes of the young Star- 

 fish, »•! being the j-ay nearest the madre- 

 poric opening. 



s. Actinal surface. 



1 1 t. Tentacles or water-system lobes of the young 

 Starfish. 



t'. Odd terminal tentacle. 



t". Ambulacral tube. 



O-l^. First to fifth lobes of the water system, corre- 

 sponding to the first to fifth ami -lobes of 

 the young Starfish (j-'-?-5). 



u. Lateral amliulacral plates, surmounted by 

 spines. 



u'. Median ambulacral plates, carrying very small 

 spines. 



w. Water-tube upon which the abactinal area de- 

 velops. 



w'. Water-tube communicating with the madre- 

 poric opening, upon which the actinal area 

 is developed. 



1-23. Astcracanthion pallidus, continued. From Alexander Agassiz, Embryology of the Starfish, 1864 (Agass. 

 Cont. Nat. Hist. U. S., V.), Pis. V., VI., VII., VIII. Mem. Mus. C'onip. Zooh, Vol. V., No. 1, North 

 American Starfishe.s, 1877, Pis. V., VI., VII., VIII. 



As the figs. 1-7 are intended to illustrate the development of the Starfish proper, the anal part alone of the 

 Brachiolaria is represented ; figs. 2-4 correspond to a Brachiolaria which has reached a stage about as ad- 

 vanced as that of PI. VII. fig. 31 ; figs. 5-7 are stages of development of the young Starfish vvliich are only 

 found on fully grown Brachiolaria, and in wliich, excepting these changes of the Starfish itself, but slight 

 modifications take place. 

 1 , 2, 6. Represent that profile of the anal part of the Brachiolaria, in successively more advanced stages, which 

 shows the water-tube upon which is developed the actinal area. 



3. Represents the opposite profile of the anal extremity of the Brachiolaria, showing the water-tnbe upon which is 



developed the abactinal area. 



4. 7. Represent the ventral side of the anal extremity of the Bracliiolaria, showing the extremities of the actinal 



and abactinal areas of the .Starfish. 



5. Represents the dorsal side of the anal extremity of tlie Brachiolaria, showing the opposite extremities of the 



actinal and abactinal areas of the Starfish. Owing to the transparency of the Brachiolaiia, either the 

 actinal or the abactinal area is always projected upon the other, when the larva is seen in profile. In 

 the dorsal or ventral views, the angle made by the actinal and abactinal areas becomes visible. 



