4 HJALMAR THEEL, NOTES ON THE DEVELOPMENT OK ECHINOCARDIUM AND PARECHINUS. 



Larvse suddendly perished. Repeated attempts were attended by the same results, 

 but I was quite unable to understand the reason why they were destroyed. The 

 oldest larva obtained had an age of 11 days and attained a length of 0,7 mm (pl. 

 I fig. 1). This figure represents a larva in the pluteus stage with four well-developed 

 arms and with traces of the posterior dorsal arms. 



The larva is characteristie by possessing a dark reddish pigment. 



During the last decade of the eighteenth century mature speeimens of Echino- 

 cardium cordatum were me t with in great abundance at a trifling depth in the bay 

 of Kristineberg. At that time they could be dredged by thousands. Seeing t hat I 

 was unable to rear young sea-urchins of this kind in iny aquaria, and being badly 

 in need of older pluteus stages and sea-urchins of different ages, 1 tried another pro- 

 cess in order to attain the main object of my efforts. Every summer of the decade 

 mentioned and at every year at the same time too, the water in the bay of Kris- 

 tineberg was dense with masses of pluteus of Echinocardium cordatum in all stages 

 of development. With a very fine-meshed tow-net I caught numbers of the larva 

 and placed them in my aquaria, wherc the water was kept in motion by mcans of 

 turbinea or pumps driven with the aid of water-works. 



This procedure was necessary in order to keep the larvse floating and to pre- 

 vent their sinking to the bottom before they had reached the desired stage of deve- 

 lopment; for a pluteus larva is always doomed to destruction when it sinks to the 

 bottow too early. 



My attempts were successful, and af ter a few days I had plenty of young sea- 

 urchins of Ecliinocardiii in cordatum in all stages of development crawling on the bottom 

 of the aquaria. As far as I know, nobody has hitherto scen Buch young speeimens 

 of Echinocardium cordatum with their dark reddish pigment, and thus J consider 

 myself entitled to publish my own drawings of them (pl. 1 figs. 2 and 3). On the 

 same plate (figs. 4 and 5) two young sea-urchins of Parechinus miliaris are figured, 

 drawn at the beginning of the' nineties from speeimens whieh were born in the 

 aquaria. These present an entirely different colour and general aspect. 



For obvious reasons I cannot enter into an explanation of the developmental 

 process of the Echinids mentioned. Considering that the time at my disposal is 



very Limited, the present paper must be eontined lo a tew pages. With regard to 



Echinocardium cordatum, I have already admitted that Lts larvse, raised in my aqua- 

 ria, did not attain an age of more t han 11 days, vi/., the first pluteus stage; and 

 concerning the earlier development of Parechinus miliaris 1 have very little to add 



lo what was know n hetore (BlTERY, .Mac BrIDE, ThÉEL ete.). But there are two 

 things whieh I intend to treat here, beeause they have a elose connection with the 

 early de\ elopiiient of t he Ivhinoderms in general and, inorcover, heeause my own 

 \ie\\s about them in some respeets do not agree with t hose expressed by other in- 



igators. The two problems in question are the following: 



