ECHINODERMATA 



455 



form the five chambers of the organ. By means of an invagination each 



shamber gives rise to one of the five primary cirri. The dorsal organ 



^ig. 224 do) is united with the chambered organ, in which, as in the 



itter, one is inclined to see the central organ of the blood-vascular 



^stem (Ludwig).^ According to Perriee, the dorsal organ is composed 



^f the genital fundament previously mentioned and a vascular plexus. 



^he latter would also take its origin from the inner enterocoelic lamella 



)f the visceral body cavity. A coalescence of the genital canals of the 



irms in the dorsal organ was conjectured even by W. B. Carpenter and 



)y LuDWiG. A number of other vascular plexuses are distinguished by 



'eerier, and their development described. They are said to be directly 



mnected with the ambulacral system. Inasmuch as portions of the 



)ody cavity also communicate with the so-called blood-vessels, the circu- 



[lation is said to be general. 



The views on the development of the nervous system are not yet clear 

 [enough to admit of a brief description. When Perriee derives parts of 

 : the nervous system from mesenchymatous elements, he is in opposition 



Fig. 225.— Lincliia mulfifora (after P. und F. Sabasin). 



to the prevailing views. [To supplement what is stated here, reference is 

 made to the work of Seeliger (No. XXVI.), which gives a very thorough 

 account of the embryology of Comatula.— K.] 



Regeneration and Division.— Starfishes possess to a high degree 

 the power of replacing lost arms. Single arms, which have become 

 detached from the disc, are again made good ; in fact, a detached arm is 

 able to develop an entirely new disc with the normal number of arms. 

 The so-called comet form of the starfish (von Martens, Haeckel) is due 

 to the newly formed parts, which at first are relatively small, bemg 

 appended, as it were, to the large arm. The mere replacement of lost 

 parts seems here to merge into a reproduction by division. Such real y 

 takes place in those forms in which the disc constricts spontaneously 



1 In the recent work of Hamann mentioned in the preceding note, the 

 connection of the dorsal organ with the chambered organ is denied, and 

 likewise the important relation of the former to the blood-vascular system 

 is regarded as being without evidence. 



