HOMOLOGIES. 147 



of the branchial lamellae. The double nature of the septal process also becomes more evident, 

 even from the fold of membrane upwards. The summit, however, is still uniformly coated by 

 the investing membrane of the branchial region j by-and-by the papilla on which it is placed 

 shortens, and the pale chitinous tips of the rods split to form the arch at the boundary. The 

 laminae of the branchial processes diminish into slender pale chitinous rods, which lie towards the 

 inner (lateral) margin of the canal, and each soon terminates in a closed extremity. Over the 

 whole of the processes just described a thick mucous layer, probably ciliated during life, is spread. 

 In ultimate structure it is glandular in appearance, being finely streaked in vertical section and 

 minutely granular. A peculiar fibrillated condition is observed in that forming the wall of the 

 branchial lamella, and also at the base of the chitinous supports of the septa. This mucous layer 

 rests upon a basement-membrane, from which numerous divergent fibres pass to the exterior 

 muscular coat of the body- wall, here and there enclosing spaces for the fatty " liver "- structure 

 found in this region. 



The foregoing account, of course, is only meant to convey a description of the framework 

 of the branchial apparatus, which in other respects has received careful treatment from the 

 excellent Russian naturalist Kowalewsky. The arrangement of the system in this form shows 

 a close approach to that of Balanoglossus clavigerus. 



Accessory Glands to the Digestive By stem. 



Anteriorly a considerable space occurs between the dorsal surface of the branchial apparatus 

 and the body-wall, which is occupied for the most part by transversely arranged sacs of the 

 yellowish fatty " liver "-tissue. These bodies are surrounded by a distinct membrane, enclosing 

 a vast number of compound fatty globules and granules, similar in minute structure to the same 

 tissue in the Nemerteans. In transverse section the contents seem to fall out of the centre, but 

 a thick layer of globules still adheres to the wall of the sac. These saccate glands occur 

 under the branchial lamellae, and generally in the space between the inner muscular layer and 

 the wall of the digestive tract anteriorly. As soon as the branchiae cease, however, they become 

 much more prominent. The digestive and respiratory functions are thus performed in one 

 chamber anteriorly, and the structure and arrangement throw considerable light on the 

 condition of the same part in the Nemerteans, where a characteristic distinction exists between the 

 two regions of the digestive system. Kowalewsky shows a folding of the branchial region in his 

 species, so that a special chamber is separated from the general alimentary cavity. The 

 digestive would therefore not intrude on the respiratory function. 



Digestive Cavity Proper. 



This chamber commences at the oral aperture, and continues in the form of a wide tube to 

 the posterior end of the animal, which, however, is incomplete in all our examples. It is supported 

 and held in position by the radiating fibres that pass inwards from the external muscular coat of 

 the body-wall. Anteriorly the glandular mucous membrane, which forms its inner coat, presents 



