354 ' EDWARD S. MORSE ON 



begin to oscillate ; the moment this oscillation ceases, the openings part and the circxilation 

 begins again. The outer side of the sinus first discharges the accumulated mass of cor- 

 puscles into the perivisceral cavity, and then the inner side of the sinus receives the outr 

 flow. The closing of these openings is always synchronous with the oscillations of the 

 shells, and it woiild seem that the contraction of the oblique and other muscles involved in 

 causing this oscillation, simply brings the dorsal and ventral shells together and the pres- 

 sure thus exerted, mechanically closes the openings and checks the flow of the current. 

 It would seem, also, that these openings are in a way controlled by definite muscles which 

 may be seen in 52: 1. These muscles have a thickened base of attachment and are appar- 

 ently animated by a nerve which branches from the auditory nerve. These openings 

 seem never to close, however, except when the shells are oscillating or are otherwise in 

 movement. In my first observations of L. lejndula, I thought I detected a flat valve 

 conti'oUiug the sinus opening and made a schematic drawing in section of what I con- 

 ceived to be the position of this valve, but later I interpreted the behavior of these parts 

 as above described. Blochmann, however, describes and figures a valve in D. lamellosa in 

 precisely the same position as 1 had supposed it to exist in L. lepkhda, though if the 

 valve really occurred in Lingula this acute observer would certainly have discovered it. 

 It is difficult to realize, unless one has seen it, the vigorous character of the flow of these 

 currents. When the damming of the current takes place and a rapid accumulation of 

 1)lo()d corpuscles piles up at the closed openings, the flood is impetuous when it starts 

 again. The volume of this flow is so great that if any special organ was implicated in its 

 propulsion it would easily be detected. No such organ, however, has been found. 



The coeloinic sinuses described in Glottidia were not so easily made out in L. 

 lepidula, owing to the dark color of the organs below. There appeared in the same 

 region, however, somewhat deeply buried, a strong ridge evidently of ciliated epithelium, 

 which I surmised to be a ciliated ridge whose posterior end turned towards the median 

 line and was widened and digitated, indicating a numbei- of lacunae branching from the 

 supposed sinus (48 : 0, 7, v. r.) . 



The result of a colored injection through the peduncular cavity of Glottidia, led to an 

 unexpected result; instead of filling the coelomic cavity and the pallial sinuses as one 

 might naturally expect it would do, the fluid ran along each side of the posterior occlusor 

 muscle, followed the median sinus dorsally, and then filled a vascular membrane which 

 lined the coelomic cavity. Not a trace of the injected fluid was found in the perivisceral 

 cavity or in the pallial sinuses. The contraction of the parts in alcohol evidently closed 

 all the openings to these regions. Much further study is necessary to illuminate the 

 mystery of the pallial and coelomic circulation of these animals. The injection, however, 

 revealed the presence of a vascular sheath lining the coelomic cavity like a peritoneum. 



