ECHINODERMATA 455 



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

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

 (Fig. 224 do) is united with the chambered organ, in which, as in the 

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

 system (Ludwict).i According to Peerier, the dorsal organ is composed 

 of the genital fundament previously mentioned and a vascular plexus. 

 The latter would also take its origin from the inner enterocoelic lamella 

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

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

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

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

 connected with the ambulacral system. Inasmuch as portions of the 

 body 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 Perrier derives parts of 

 the nervous system from mesenchymatous elements, he is in opposition 



Fig. 225. — LincHa midtifora (after P. und F. Saeasin). 



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

 made to the work of Seeligek (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, being 

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

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

 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. 



