K.) SVEN LOVEN, ECHINOLOGIOA. 



a diseoidal form and builds up a new skeleton, of two sy- 

 stems: The calycina] .system with the dorso-central disk 

 eiitire, and the coronal system of two mutuall^^ indepeii- 

 dent constituents. The five ambulacra, heterotropic from the 

 first, throughont of two columns of plates perforated by pores 

 and bearing pedicels, have their iirst-formed pairs, the primor- 

 (liaLs, coiistituting by theraselves an innermost closed eircle, 

 each pair of which is foHowed by a consecutive series of succes- 

 sively added plates, the last formed always contiguous to the 

 corresponding radial of the cal3'x. The five interradia, alterna- 

 ting with the ambnlacra. begin ontside the primordial eircle 

 of these with a solitär}'' plate, which is followed by a donble 

 eolnmn of sneeessively added plates, the last-formed of which 

 is contiguous to the corresponding eostal of the calyx. The 

 animal moves about by the aid of five large and powerful 

 suckers based upon the outer ends of the radials. It takes no 

 food from without, being astomous as well as aproctic, its 

 alimentary canal is functionless and it subsists on the stores 

 of cellulai' matter laid up in its tissues during the previous 

 pluteal freely feeding existence. But within the central part 

 of the envelope it prepares for the imago new feeding-instru- 

 ments, a pharyngeal system of jaws and teeth, and an excre- 

 tory apparatus. While this is doing the disappearance of the 

 provisional suckers, and a line of separation appearing between 

 the primordial ambulacrals and the following pairs, announce 

 the approach of the final state. 



It nuw follows to compare corresponding stages among 

 the families of the Ectobranchiata. The young of these, as far 

 as hitherto described, all derive from free-swimming plutei and 

 belong to the Arbaciidee, Echinidtf, or Echinoraetridae. ' 



To some northern species of the Echinidpe a young spe- 

 cimen 0,6 mm. in diameter seems referable that had been caught 

 b}- the towing-net in the North Sea and preserved in spirits. 

 Of this specimen figures were drawn by Mr AVestergren with 

 the utmost care and not in the least diagrammatic, and published 

 in former works; I repeat four of them in the woodcut an- 

 nexed. They evidently represent the exteriör of the Echinid 

 as it is after the last of the calcified rods of the Pluteus has 



See above p. 1. 



