30 BULLETIN OF THE 



resemble those of Ludwig on Asterina,* and Loven's figures of A. gla- 

 cialis,1[ but differ somewhat from Agassiz's. A. Krohn $ was one 

 of the first correctly to figure the situation and early form of the 

 oral ambulacrals of the starfish in young stages in its growth. His 

 figure of the ten first formed oral ambulacral plates in the starfish 

 found in Bipeunaria correspond closely with those of Asterias which I 

 have represented. He also figures the spines of the terminals, but does 

 not represent the terminals as they exist in Asterias. 



Sir Wyville Thomson's figure and description§ of the early forms of 

 the ambulacral rafters of Asteracanthion violaceits closely resembles what 

 I have seen in Asterias. His figure of the oral ambulacrals and the 

 ambulacral rafters corresponds with mine. There is not as close a 

 likeness in the plates of the abactinal side which he has figured and 

 my own. The first dorsal seems more prominent in one than in the 

 other. Both of his figures, represented from the actinal and abactinal 

 hemisomes, are regarded as important contributions to our knowledge 

 of the early form of the calcareous plates of Asteroids. 



Metschnikoff j| has published very instructive figures of the young 

 and stellate forms of a starfish. In Plate XI. fig. 8, he represents the 

 earliest form of the ambulacral orals about as they appear in Asterias. 

 They have here the form of simple calcareous spicules. The spines of 

 the terminals in this stage are also well showii Another figure of a 

 young starfish by the same author (PI. XII. fig. 1, A) represents five 

 terminals, an inner row of six genitals, and a dorsocentral. The mad- 



* It may be borne in mind that the mouth of Asterias is " ambulacral," i. e. 

 formed for the most part of modified ambulacrals, while Asterina is classified as 

 " adambulacral," — mouth formed of both ambulacral and adambulacral. It is 

 consequently necessary that the young stages of Asterina have adambulacral 

 calcifications distinct from ambulacral in the formation of oral plates. It would 

 seem from Ludwig's figure (fig. 98) and his lettering as if it was formed in this way. 

 In Asterias, however, similar plates are formed from the interradial ends of the 

 ambulacrals, and not as separate calcifications. If I am right in my observations, 

 it would seem that Asterias has an ambulacral mouth from the early stages of 

 growth. 



t Etudes sur les Echinoide'es. K. Svensk. Vetensk. Akad. Handl., Stockholm, 

 Vol. XL Pt. II. 



i. Krohn, August. Ueber die Entwickelung der Seesterne und Holothurien. 

 Arch. f. Anat. Physiol. u.Wiss. Med., 1853. 



§ Thomson, C. Wyville. On the Embryology of Asteracanthion violaceus, 

 Quart. Jour. Mic. ScL, I., 1861. 



|| Metschnikoff, E. Studien fiber die Entwickelung der Echinodermen und 

 Nemertinen. Mem. Acad. Imper. Sci. St. Petersbourg, Vol. XIV. No. 8. 



