228 THE ORGANIZATION 



gills of ordinary fishes, into the general cavity (ac) of the body, 

 and thence passes out of the abdominal pore, (ap,) to the exterior 

 world. The true intestine (i) commences with a moderate aper- 

 ture () at the posterior end of the branchial gullet, and pro- 

 ceeds to its termination (i 1 ) in a nearly direct line. Near its 

 beginning a saccular organ (Iv, lu l ) which is thought to perform 

 the office of a liver, opens into it. 



The circulatory system can hardly be said to possess a heart. 

 The oval enlargement (A) in the diagram is an exaggeration, 

 merely to render conspicuous the position in which the heart 

 belongs. The whole system of vessels is said, by those who 

 have examined the animal in a living state, to contract from one 

 end to the other. According to this diagram the blood courses 

 from the central cavity, heart, (A,) in a backward direction, in a 

 single vessel (/t 5 ) along the lower side of the body to the tip of 

 the tail, and then, doubling upon itself, it passes along the upper 

 median line (A 6 to A 4 ) of the general cavity of the body, and 

 directly over the gill-chamber (b to b l ) into the head. At the 

 fore part of the gill-chamber it forks (at A 4 ) and sends a branch 

 into each of the ciliated palate-like bodies (I, II) of the buccal 

 cavity ; and after penetrating to the tips of these, the two 

 branches double upon themselves, and, returning, (A 3 ,) unite 

 again into one vessel (A 2 ). This continues its course along the 

 dorsal median line (A 2 ) further into the head to a point over the 

 anterior edge of the mouth, and there, by two vessels, joins 

 the return current, (A 1 ,) which passes along the lower middle line 

 of the gill-chamber to the heart. The circulation is further com- 

 plicated by intermediate currents which pass from the upper 

 median vessel (A 4 ) directly downwards in smaller channels (br) 

 which lie between the slits (bo) of the gills, and empty into the 

 lower median vessel (A 1 ) where it joins the stream coming 

 from the head. In full-grown specimens of the Lancelet there 

 are as many as fifty of these transverse branchial vessels. 



The more recent investigations of Quatrefages differ* in their 



* Quatrefages, Voyage en Sicile, vol. n. p. 12, and Annales des Sciences 

 Naturelles, 1845, vol. iv. 



