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



19 



PLATE VI. 



Development of Asteroidea, continued. Figures from Hubert Ludwig, Louis Agassiz, Michael 

 Sars, C. Wtville Thomson, Johannes Muller, and J. Koren and D. C. Danielssen. 



1-11. Asterina gihhosa, continued. From H. Lmhvig, Morphologische Stiulicn an Echinodermen II., 2 Heft, 

 1882. Zeits. f. Wiss. Zool., XXXVII., Pis. VII., VIII. 



Ai- First ambulacral jilate. 



A.2- Second ambulacial plate. 



A dy First adambulacral plate. 



A 1I2. Second adambulacral plate. 



Af. Anal opening. 



£ I. Blood system. 



C. Centrodorsal plate. 



v. Digestive cavity. 



Ec. Enteroccelum. 



F. Terminal tentacle. 



Fy First pair of tentacles. 



F2- Second pair of tentacles. 



ff c. Hydroccelum. 



Ja. Interambulacral plates. 



Jm. Intermediate plates. 



3. 



6 



JH^, Jr..,, J Ih, JJ!i, J Ik- First to fifth interradial 

 plates. 



v]/ 1 . Interradial space of the larval organ. 



■\f m. Interradial space of the madreporic plate. 



M. Mesentery. 



Afs. Mesoderm. 



P. Dorsal pore. 



S s. (Esophagus of Starfish. 



St. Stone canal. 



Ti, ^2, Ts, Ti, T'j. First to fifth terminal plates. 



1, 2, 3, 4, 5, denote the hydrocrelum and ambula- 

 cral lobes. 



/, II, in, IV, V, denote the antianibnlacral arm- 

 lobes. denotes the up]ier extremity ; f", 

 the lower ; V, the anterior ; //, the poste- 

 rior ; L, left ; 1!, riglit. 



11 



1. Larva at the end of the ninth day, seen from the dorsal side of a young Starfisli. Tlie abactinal region is rep- 



resented as transparent, to show the five lobes of the digestive cavity, the centrodorsal plate C, the five inter- 

 radials JBj-J R^, and the five terminal plates Tj- 7 5. The remnant of the larval organ ( the brachiolarian 

 arms) is represented by a. 



2. Larva of tlie tentli day, seen from the anterior extremity ; the optical section passes through the lobes 1 and 



3 of the hydroccelum ; a b, remnants of the larv.al organ. 



Transverse section of a larva in the stage of fig. 2. Tlie amliulacral arm lobes 2 and 3 liave been cut longitudi- 

 nally. 



A yonng Starfish at the end of the tenth day, after the reduction of the larval organ rr ; the mouth of the Star- 

 fish is not yet formed. 



Young Starfish of the tenth day, seen from the abactinal side ; a, larval organ ; 4, 1, iiitcri-adial space of tlie 

 larval organ ; i>tn, interradial siiace of the madrej5oric body. 



Section across a young Starfish of the eleventh day, close to the actinal side. The water-ring is not yet closed ; 

 at a are the two diverticula of the water system, which unite in a subsequent stage ; the section passes 

 through the three-lobed digestive cavity, Ss ; this does not yet open externally. 



7. Exterior view of the soft parts of an arm of a young Starfish, in the thirteenth day. iV, rudimentary nervous 



ring ; B, swelling at the base of the terminal tentacle, where later an eye develops. 



8. The same as fig. 7, to show the course of the ambulacral canal, the tentacles, and their position with respect 



to the terminal, the amhuhicral, and the interradial plates. 



9. Starfish of the sixteenth day, seen from the actinal side, to show the general arrangement of the hard parts. 



0. .\ young Starfish of the sixteenth day, seen from the abactinal side, about in the same stage as fig. 9. Show- 

 ing the arrangement of the plates of the abactinal side, the anal opening Af, the odd terminal tentacle F, 

 extending beyond the edge of the disk ; .?, the young spines. 

 Taken from a young Starfish forty-two days old. The abactinal surface is removed, .showing the five blind 

 pouches of the alimentary canal, which begin to fork at the extremity to form the five pair of digestive 

 coeca of the old Starfish ; M, rest of the larval mesentery ; Sj', the five interbrachial septa ; Bs, the inter- 

 radial ececum of the end of the alimentaiy canal. 



