LIVING BRAOHIOPODA. 349 



this nerve passes through the muscles above mentioned, it enters the posterior occlusor 

 muscle on its inner face and there terminates in a ganglion giving off numerous twigs 

 (52 : 4, 5) . 



The marked difference between the oblique nerves of Lingula and Discinisca is seen 

 in the fact, that, while in Lingula the nerve runs along the inner surface of the various 

 muscles it encounters, sending twigs only to the muscular fibers within, in Discinisca the 

 nerve not only passes directly through the muscles in its path but finally enters the 

 posterior occlusor muscle where it terminates in the ganglionic enlargement above 

 described. 



In D. stella, owing to its diminutive size, but little information was secured regarding 

 its nervous system. A central ganglion was seen on the anterior body wall below the 

 mouth. There was no bilateral division or swelling of this central nerve ; it was simply a 

 gaugliouic area from which were given off two diverging branches dorsally and two 

 diverging ones veutrally with a median one ventrally ; these were all branched (52 : 3, 3) . 

 In T. coreanica, an elongated oval ganglion is seen just below the mouth. This ganglion 

 shows no bilateral division. From this gauglionic center, delicate nerves run off in 

 bi-symmetrical arrangement to the pallium as well as laterally and ventrally (52 : 6) . 

 The possible function of the pallial coeca as organs of tactile impression has already been 

 alluded to. 



PALLIUM. 



A consideration of the pallium cannot be made without including the branchia as 

 seen in the gill ampullae of Glottidia, the lacunal circulation, and finally a discussion of 

 the vesicular organ recognized as the " heart of Hancock." The pallium is the principal 

 respiratory organ, and the views of Cuvier, Vogt, and Owen were quite correct as to the 

 nature of this highly vascular membrane. 1 Nor can we consider the pallium apart from 

 the shell, for both hard and soft parts of this external covering belong literally to one and 

 the same structure, and this has been recognized by students of the subject. Beyer ('86) 

 in his interesting memoir on Glottidia, after describing in detail the structure of these 

 parts as revealed in stained sections, says, " Their continuity renders the conclusion 

 almost obvious, namely, that they are identical in structure ; in other words the so-called 

 horny layers of the shell of Lingula are nothing more nor less than a supporting sub- 

 stance." Every investigator of these parts has been baffled in an attempt to separate the 

 shells from the lining membrane below. 



1 There is no reason to doubt that the brachia, and other parts where the membranes are sufficiently thin, are instrumental 

 in the work of oxidizing the blood, though Schulgin found the cirri of Cistella closed at their point of attachment and 

 asserts that there was no evidence of a circulation of fluid within. 



