LIVING BRACHIOPODA. 327 



firm, indicates the presence of mucous glands in the peduncle, for in no other way could 

 these sand tubes be fabricated into symmetrical and somewhat durable sheaths such as 

 we find in Glottidia. When the animal is living in the open sand in the sea, the tube has 

 a certain compactness and s^yrnrnetry; but when confined in a shallow bowl, the animal 

 forms a loosely constructed burrow of sand which is made adherent to the bottom of the 

 bowl and often encloses part of the shell beside. 



When the peduncle is broken, the mutilated end contracts into a bulbous form and 

 gathers about it a globular ball of sand whose walls are much thicker than those of the 

 normal sand tube. An injury to the peduncle of L. lepldula makes plain its structure. 

 There is first a thick outer tube having little structural character, a middle tube, or 

 sheath, having strong transverse folds on the outside, which alternate with the irregular 

 annulations of the outer tube, and, finally, an inner tube with delicate encircling and 

 longitudinal muscular fibres. When the peduncle is broken, the inner tube bulges like 

 a button beyond the severed end, and in this attitude it presents a curious ribbed and 

 turbinated appearance caused by the contraction of these two sets of muscular fibres 

 (43: 1, '!} The action of the longitudinal muscles contracting in the centre, with the 

 contraction of the outer encircling fibres, gives this button-like end the peculiar ribbed 

 appearance shown in the figures. When only a slight contraction of the fibres takes 

 place, the button-like end is smooth (43: 3). Whether the undue enlargement of the 

 outer sheath is caused by the unnatural contraction of the inner tube or the absorption 

 of water, I do not know. 



In Glottidia the peduncle has the same structure, though I have never observed the 

 turbinated appearance of the end. Minute transverse striae mark the surface of the 

 peduncle, and areas of minute dots are seen which may be mucous pores, and I may add 

 here that in life the peduncles of Lingula and Glottidia are exceedingly mucous, the 

 mucosity extending to the body as well. The peduncle consists of a thick outer wall 

 irregularly annulated, though this appearance is not the result of a true vermian annula- 

 tiou. In certain states, the peduncle in Glottidia is so symmetrically and structurally 

 annulated that when I first saw this condition I was almost inclined to look for setae. 

 Within tin's thickened tube is a lining membrane and within this is a tubular sheath held 

 to the lining membrane by delicate connective tissue. This is shown in 43 : 0, where the 

 body has decayed and separated from the peduncle ; the inner delicate tube is seen held 

 in place, by threads of tissue. In this figure the current is indicated running down 

 toward the end of the peduncle and back on both sides. In 43 : 7 there seems to be a 

 ciliated rod, on each side of which the current courses in opposite directions. On the same 

 plate, 4, 8, 9, the current is shown running down on one side and back on the other side. 

 In 41: 16 is shown the appearance of the inner tube as it is drawn away from the outer 



