THE DEVELOPMENT OF BALANOGLOSSUS. 



539 



the true nature of Salanoglossus, the vascular system con- 

 sists of a dorsal and a ventral vessel. At the posterior end 

 of the branchial region the former divides into a superior and 

 an inferior dorsal, and two lateral, trunks. The superior 

 trunk passes forward, and, at the anterior end of the body, 

 divides into two descending branches, which unite with the 

 ventral trunk. The inferior dorsal trunk supplies the bran- 

 chiae, of which the lateral trunks are the eflFerent vessels. 



For the pharyngeal branchiae of JBalanoglossus, the only 

 parallels to be found are among the Tunicata and the Verte- 

 brata. On the other hand, the larval form of this anomalous 

 creature is generally Annelidan or Turbellarian, with very 

 close and special resemblances to the Echinop^edia of some 

 J5c'A inoderm ata. 



The young of Balanoglossris was first observed by Miiller, 

 who called it Tornaria, and regarded it (as did all succeeding 

 observers until its true nature was discovered) as an Echino- 

 derm-larva, on account of its extraordinary resemblance to 

 the larvae of Star-fishes (Fig. 153, I.). 



Fig. 15^.— Balanofflossus. (After A. Agassiz.) 



I. The Tornaria larva, Bide-view (about tV of an inch Ion?): a, anns; 5, vessels 

 leadincf to the dorsal pore (d) from w, the eac of the water-vascnlar system ; w', 

 prolongation of the sac; h, heart; i, intestine; s, stomach; o, cesopliasfus: m, 

 mouth; u, u', lobes of the alimentary canal; mb, muscular band running from 

 the eye-speck (e) to the water-vascnlar sac. 



n. A young Balatioglossiis—leitQTB as before, except g, the first formed branchial 

 stigmata. 



ni. A more advanced Balanog'.ossus : e, the collar; p, the proboscis. 



It is an elongated ovoid body, provided with three bands 

 of cilia, one of which is prae-oral, while the other two are 



