348 EDWARD S. MOUSE ON 



proximity to the nerve, a small circular body is shown which the author simply indicates 

 as "tubercles, function unknown." It has occurred to me that these might be aiiditory 

 vesicles, as they occur just where they might properly lie found, ''^i this supposition could 

 be established, then the Testicardine as well as the Plcanhne In-acliiopods may be 

 considered as having auditory organs. That Glottidia and Lingula are sensitive to light 

 there can be no doubt. They seem sensitive to the interruption of light that falls upon 

 them and withdraw beneath the sand with a (piick jerk. Any pigmentation sensitive to 

 light, in the al)ove genera at least, woidd naturally be looked for on those parts of the 

 animal exposed above the sand, and oni' would expect to find these areas about the 

 anterior portions of the pallium. Schulgin finds in Cistella an accumulation of pigmen- 

 tary epithelia which at certain distances are found on the periphery of the pallium, and he 

 is inclined to b&lieve that tliese areas pi-oljably indicate rudimentary organs of sense; 

 namely, the eyes. These parts, he says, receive nerve fibers. 



In Glottidia the anterior margins of the pallium, both dorsal and ventral, are thrown 

 into two deep and distinct folds, one on each side of a median line. The space between 

 the folds and the shell has light brown, interrupted, and sinuous striae ; the outside of this 

 area is marked by dark brown dots, while the iinier edge is marked by a dark brown stripe. 

 The function of these folds in connection with the setal tubes has already been alluded to, 

 but this definite pigmentation of the pallium in just the position where we might expect 

 to find areas sensitive to light certainly suggests a function of this nature, and Blochmann 

 has shown that a number of nerve branches run to this region in L. anatlna ; and so I 

 venture the suggestion that these rich brown, pigmentary areas may function as sensory 

 organs for the perception of light (39: 5, 6; 51, 15, 10). Lingula lejndula shows precisely 

 the same pallial folds richly pigmented. In all my drawings from life these anterior folds 

 are seen, and I am inclined to believe that in L. lejndula, these folds appear only when 

 the setal tubes are formed, and in this way, if the pigmented parts are sensitive to light, 

 these parts are exposed at just the time when tlie animal is in an attitude to profit by 

 this sensitiveness. In Glottidia, an adjustment of the setae is made, analogous to that of 

 L. lepidula when it forms the setal tubes, and here again the strongly pigmented folds of 

 the pallium become conspicuous. 



In JJisc.inisca Umiellosa, the oblique nerves are found free in the coelomic cavity, as in 

 the LimjuUdae. They enter this cavity between the first anterior occlusor and the 

 lateralis muscle. Joubin, curiously enough, does not figure this nerve. Blochmann, not 

 only figures it, but represents it correctly as passing through the obliquus anterior and 

 obliquus posterior muscles, but traces it no farther. He represents the posterior occlusor 

 as being furnished with a twig from the lateral dorsal nerve, which is a peripheral nerve 

 following the lateral wall of the coelomic cavity. My own observations show that after 



