226 jiEPORT — 1851. 



great beauty. At this point the true biliary apparatus begins ; it is the source 

 and cause of the yellow colour. The ultimate glandular cells of the liver are 

 disposed in minute groups, square or round, or oblong, according to the 

 figure of the space enclosed by the ultimate capillaries of the vascular mesh. 

 No part of the structure of the Annelid is so profusely supplied with blood 

 as the parietes of the biliary segment of the intestine. There are here de- 

 tectable in all species elaborate reticulations, while a blood-vessel can only 

 with difficulty be observed in other parts of the body. The group of oil-cells 

 contained in a separate involucrum, just large enough to occupy a mesh of 

 this rete mirabile, constitute the liver in real fact. This little group of oleous 

 molecules, floating in a semi-fluid substance of a brilliantly yellow colour, 

 represent the real elements of the biliary organ. In no instance, in any 

 species, is any departure from this type of structure exhibited ; the liver, 

 therefore, in these animals is diffused under the character of a bright yellow 

 flocculent stratum, over nearly the whole extent of the alimentary canal. It 

 is most developed near the raid-body, the elementary glandules becoming 

 gradually more distinct and removed from each other in proportion as the tail 

 is approached. In the Serpulidm, Sabellce, and Amphitrita, the rectal por- 

 tion of the intestine dilates, becomes greater in diameter, and the orifice itself 

 is a capacious opening. It is not difficult, in this provision, to perceive the 

 manifest indications of design; by it every obstacle to the free escape of the 

 contents of the intestine is removed ; no impediment, such as that would be 

 if the orifice were guarded by a sphincter muscle, is offered to the action of 

 the cilia, upon the efficient operation of which the well-being of the little 

 cell-prisoner so completely depends. 



The intestinal system of the Terehellce (fig. 51) differs in several material 

 respects from that of the Serpulm and Sahellce. The oesophagus, a strong 

 muscular tube, in this genus is remarkably long ; it is not however in the 

 least degree protrusile. These worms are distinguished for the strength and 

 muscularity of the lips, which are superiorly and inferiorly placed with re- 

 ference to the mouth. These appendages to the mouth are well-adapted in 

 a mechanical sense for swallowing mud, soft earth, clay, and dirty water. 

 During their slow, awkward and tedious locomotion, the Terebellce carry the 

 mouth close to the ground, the lips being actively at work in turning up 

 the soft soil. The posterior half (fig. 51 a) of the oesophageal tube is em- 

 braced by a bright yellow glandular mass, differing from the ordinary biliary 

 layer in being composed of larger, more prominent, lobulated masses. It is 

 quite indisputable, both from its structure and situation, that this is a true 

 glandular structure, and that it supplies a secreted product tributary to di- 

 gestion. From this structure the lesson may be drawn, that the comparative 

 physiologist should not feeKoo confident in assigning a biliary function to 

 any structure in the inferior animals merely because it possesses a yellow co- 

 lour. Other glandular structures generate the yellow pigment, while in- 

 stances might be multiplied in considerable number, in which true biliary 

 organs are not distinguished by a yellow colour, but by a green, or dark 

 brown. In the progress of our studies in the Annelidan class of Inverte- 

 brata, the varieties mentioned in the mere colour of the liver will soon fall 

 under description. From its position around the posterior end of the oeso- 

 phagus, the glandular organ in the TereheUa. supplies probably a fluid bear- 

 ing some analogy to saliva, and yet it is far too elaborate a structure to be 

 dedicated exclusively to a mere salivary function. Here again is an illus- 

 tration of the difficulty of determining the strict meaning of an organ on the 

 mere ground of a similarity in anatomical relations ; no less fallacious is that 

 resting on analogy of ultimate structure. These physiological difficulties are 



