624 PISCES. 



branchial canal, as it is called by Muller, which, being continued back- 

 wards, terminates in the commencement of the alimentary canal (e) . 



(1671.) The branchial chamber is supported by a very singular sort 

 of framework, first described by Retzius and Goodsir, and subsequently 

 more in detail by Professor Muller. It consists of a considerable number 

 (variable according to the age of the animal) of thin rib-like processes, 

 which are united together superiorly, but quite free below, so that they 

 constitute a series of semicircular arches, united together by transverse 

 cartilaginous bands, so as to roof-over the branchial vault. This solid 

 framework is lined internally with a kind of mucous membrane, which, 

 however, is not continuous from rib to rib, and consequently does not 

 fill up the intercostal spaces, but leaves a fissure between each pair of 

 the cartilaginous arches, so that in adult specimens there are as many 

 as a hundred of these branchial fissures or more ; nevertheless, as the 

 whole branchial chamber, as well as the margins of these fissures, which 

 are extremely narrow, are closely set with vibratile cilia, it is very diffi- 

 cult to perceive their existence, which, indeed, was denied both by 

 Eathke and Goodsir. 



(1672.) On placing a living Amphioxus in water coloured with indigo, 

 and observing it with a microscope, it is apparent that the coloured 

 particles that enter the branchial chamber are driven by the ciliary 

 action, partly towards the alimentary canal, and enter the intestine, 

 while another part traverse the branchial fissures, and thus enter the 

 abdominal cavity, where there is no longer any ciliary movement, but 

 the water which flows into it unceasingly through the branchial appa- 

 ratus forms a continuous current, which finds an exit through the 

 abdominal pore (c), the margins of which exhibit ceaseless movements 

 of contraction and dilatation. Behind the abdominal pore, the cavity of 

 the abdomen is impermeable to water, and closely embraces the terminal 

 portion of the intestine. 



(1673.) The cavity in which the branchial apparatus above described 

 is lodged contains likewise the greater portion of the alimentary tube, 

 as well as the liver, the generative apparatus, and the kidneys ; so that, 

 in fact, it performs the functions both of a respiratory and abdominal 

 cavity. 



(1674.) The digestive system of this singularly-organized being 

 presents, in many respects, a very degraded type of structure. The 

 branchial chamber above described terminates posteriorly in a short and 

 narrow canal, which is the oesophagus. This opens into a wider intes- 

 tine, which is always easily distinguishable, owing to the green colour 

 of its parietes. A little beyond the termination of the oesophagus, there 

 is appended to the intestine a long caecum (/), almost as capacious as 

 the intestine itself, which is supposed by some to represent the liver, 

 here reduced to its simplest possible condition. Muller, however, adds 

 that the whole of the intestinal walls, which are lined with a greenish 



