Royal Society. 233 



aperture, its inferior portion being constituted by a mere commis- 

 sural band. 



M. Gratiolet, however, states with justice that the inferior side of 

 this collar is the thicker, and I find both in Rhynchonella and in 

 Waldheimia that it constitutes, in fact, a distinct oblong ganglion, 

 of a brownish colour by reflected light. From its extremities com- 

 missural branches pass round the mouth, while other cords are 

 distributed to the arms, to the superior and inferior pallial lobes, 

 and to the so-called hearts. The nerves are marked by fine and 

 distinct longitudinal striations, and can be traced to the margins of 

 the pallial lobes, where they become lost among the muscular fibres 

 of the free edges of the mantle. 



Structure of the Arms. — I have not been able to convince myself 

 of the existence of that spiral arrangement of the muscular fibres of 

 the arms which has been described in Rhynchonella and Waldheimia. 

 I have found the wall of the hollow cylinder of the arm to be con- 

 stituted (1) externally, by an epithelium, within which lie (2) the 

 reticulated canals, which have been already described ; (3) by a de- 

 licate layer of longitudinal or more oblique and transverse fibres, 

 which are probably muscular, and (4) internally by a granular 

 epithelial layer. 



In Rhynchonella the bases of the arms are terminated by two con- 

 siderable sacs, which project upwards into the visceral cavity. Have 

 these the function of distending and so straightening the spirally 

 coiled, very flexible arms of this species ? 



Affinities of the Brachiopoda. — All that I have seen of the struc- 

 ture of these animals leads me to appreciate more and more highly 

 the value of Mr. Hancock's suggestion, that the aflfinities of the 

 Brachiopoda are with the Polyzoa. As in the Polyzoa, the flexure of 

 the intestine is neural, and they take a very natural position among 

 the neural mollusks between the Polyzoa on the one hand, and the 

 Lamellibranchs and Pteropoda on the other. 



The arms of the Brachiopoda may be compared with those of the 

 Lophophore Polyzoa, and if it turns out that the so-called hearts 

 are not such organs, one difference will be removed. 



In conclusion, I may repeat what I have elsewhere adverted to, 

 that though the difference between the cell of a Polyzoon and the 

 shell of a Terebratula appears wide enough, yet the resemblance be- 

 tween the latter with its muscles and the Avicularium of a Polyzoon, 

 is exceedingly close and striking. 



" On the frequent occurrence of Indigo in Human Urine." By 

 Arthur Hill Hassall, M.D. 



From the present communication it appears that the occurrence 

 of indigo in human urine is more common than the author was led 

 to anticipate from his first inquiries. 



The author furnishes additional proofs of the blue colouring matter 

 in question being really indigo, by converting it into isatine and 

 aniline. 



Contrasting its chemical and physiological relations with hsema- 

 tine and urine pigment, he shows that indigo is closely allied in its- 



