288 Royal Society. 



forming a sort of free caecum in the visceral cavity. My reasons for 

 believing that it is a free caecum are these : — in the first place, no 

 anal aperture can be detected in the mantle cavity, either on the 

 right or left sides, although the small size of the animal allows of 

 its being readily examined uninjured, with considerable magnifying 

 powers. 



Secondly. If the shell be removed without injuring the animal 

 and the visceral cavity be opened from behind by cutting through its 

 walls close to the bulb of the pedicle, it is easy not only to see that 

 the disposition of the extremity of the intestine is such as I have de- 

 scribed it to be, but by gentle manipulation with a needle to convince 

 oneself that it is perfectly unattached. And in connexion with this 

 evidence I may remark, that the tissues of the Brachiopods in general 

 are anything but delicate ; it would be quite impossible for instance 

 to break away the end of the intestine of Lingula from its attach- 

 ments without considerable violence. 



Thirdly. If the extremity of the intestine, either in Rhynchonella 

 or in Waldheimia, be cut off and transferred to a glass plate, it may 

 readily be examined microscopically with high powers, and it is then 

 easily observable that its fibrous investment is a completely shut 

 sac. In Rhynchonella the enlarged caecum is often full of diatoma- 

 ceous shells, but it is impossible to force them out at its end, while 

 if any aperture existed they would of course be readily so extruded. 



However anomalous, physiologically, then, this caecal termination 

 of the intestine in a molluscous genus may be, I see no way of 

 escaping from the conclusion that in the Tarebratulidce (at any rate 

 in these two species) it really obtains. There are other peculiarities 

 about the arrangement of the alimentary canal, however, of which I 

 can find either no account at all or a very imperfect notice. 



The intestinal canal (figs. 1 and 2 b, d, e) has an inner, epithelial, 

 and an outer fibrous coat ; the latter expands in the middle line into 

 a sort of mesentery, which extends from the anterior face of the 

 intestine between the adductors, to the anterior wall of the visceral 

 chamber, and from the upper face of the intestine to the roof of the 

 visceral chamber ; while posteriorly it extends beyond the intestine as 

 a more or less extensive free edge. I will call this the mesentery {/). 



From each side of the intestinal canal, again, the fibrous coat gives 

 off two ' bands,' an upper {g), which stretches from the parietes of the 

 stomach to the upper part of the walls of the visceral chamber, 

 forming a sort of little sheath for the base of the posterior division 

 of the adductor muscle, which I will call the g astro -parietal band ; 

 and a lower, which passes from the middle of the intestine to the 

 parietes, supporting the so-called ' auricle.' I will call this the ilio- 

 parietal band {h). 



The ilio-parietal and gastro-parietal bands are united by certain 

 other ridges upon the fibrous coat of the intestine, from whose point 

 of union in the middle line of the stomach posteriorly, a pyriform 

 vesicle (w) depends. 



The mesentery divides the liver into two lateral lobes, while the 

 gastro-parietal bands give rise to the appearance that these are again 



