ON THE BRITISH ANNELIDA. 227 



not encountered in the anatomy of the higher and more specialized or- 

 ganisms ; but in inferior forms, fusions of organs and substitutions of func- 

 tions are frequent in their occurrence. 



In the TerehellcB, the CESophagus is succeeded by a segment of the canal, 

 distinguished by the absence of the yellow colour. It presents the charac- 

 teristics of an elongated gizzard (fig. 516); the parietes of this portion are 

 muscular and dense, and little vascular. It is generally found on examina- 

 tion to be devoid of contents ; the alimentary substance does not stop or 

 lodge in it. This gizzard-like portion is followed by the true biliary in- 

 testine, divided by constrictions into annular segments, equalling those of the 

 integument in number, although not similar in character. In intimate struc- 

 ture this portion answers with exactness to the Annelidan type. The bile- 

 gland consists essentially of minute lobuli of oleous molecules (fig. 51 c), en- 

 veloped in a common capsule, surrounded by a blood-vessel, and opening into 

 the intestine by a common orifice. It is remarkable that in these animals 

 there should exist such a monopoly of blood in the biliary apparatus, while 

 so little blood-proper is observed in the body as a whole. From this circum- 

 stance it may be reasonably argued that the bile in these inferior forms of 

 organization unites in itself some other function in the work of primary 

 assimilation than that limitedly defined office which is discharged by the bile 

 of the higher animal. The biliary glandular layer of the intestine becomes 

 thinner and thinner as the posterior termination is approximated ; and the 

 contents acquire more and more the excrementitious character. The rectum, 

 as in the Terebella, expands, and ends in a large anal outlet ; the interior of 

 this part of the intestine exhibiting, as in kindred genera, a rich lining of 

 vibratile cilia. 



Arenicola Piscatorum lives almost exclusively on sand. The ' coils ' ob- 

 served on soft sandy shores, supported always by a substratum of clay, are 

 caused by these familiar ' lugs.' The sand is swallowed as the animal 

 advances through the soil, traversing the whole extent of the body ; and 

 yielding up for the purposes of digestion what it happens to contain of 

 organic matter, it is finally rejected under the form of sand-coils, remarked 

 so commonly on the sea-shore. Arenicola is capable of exserting the pha- 

 ryngeal membrane to some distance beyond the extremity of the head 

 (fig. 52 a). When thus protruded it answers all the mechanical purposes of 

 a proboscis, although devoid of hard parts, or jaws. The mucous surface, 

 both of this part and of the oesophagus to some distance inwards, is thickly 

 beset with minute glandules projecting in relief above the surface. They 

 contribute the first organic fluid to the action of which the food is sub- 

 mitted. Deglutition is impracticable in this worm, unless the sand be almost 

 saturated with water ; dry sand cannot be swallowed, and if too wet, it is not 

 well grasped by the proboscis. 



The oesophagus (fig. 52 b) is a strongly muscular tube, surrounded by a 

 frame-work of four longitudinal vessels, with detached smaller branches for 

 the nutrition of this segment of the canal ; compared, however, with the in- 

 testinal segment of the canal, the oesophagus is scantily supplied with blood. 

 At the point of junction between the oesophagus and true intestine, and just 

 anterior to the cardiac centre of the blood-system, may be seen two pyriform 

 bodies (fig. 52 c), hollow in the interior, and communicating by a large 

 opening with the channel of the oesophagus. They are sometimes found to 

 contain a greenish yellow fluid, which tinges the surface over which it flows. 

 The microscope entirely fails to discover in the parietes of these diverticula 

 of the oesophagus, any evidences of glandular formation, — nothing to throw 

 light on the mechanism of their secreting function. It may be affirmed with 



q2 



