SEA-FISHERIES LABORATORY. 497 
With regard to the function of this well-developed 
organ, it is difficult to see that it ean be any other than 
a water-testing, either smell or taste organ, yet this sense 
is generally ascribed to the osphradia, and it is difficult 
to understand the presence of two organs doing the same 
work, situated very close to one another, and yet having 
a different structure. 
The histological structure is remarkably like that of 
the “Seitenorgane”’ described by EHisig (43) in the 
Capitellidae, and Thiele himself supposes that the 
function, like that of these organs and the lateral line of 
fishes, is the perception of vibrations in the water, though 
no experimental evidence is put forward. 
Tur Kyrs..-No organs of Pecten, nor of the Lamelli- 
branchs in general, have given rise to more discussion 
with regard to details of structure than the eyes; and as 
one would expect, these remarkable organs, which are so 
prominent, glittering like minute diamonds set amidst a 
forest of tentacles, attracted the attention of early 
naturalists. They were first described by Poli, as far 
back as 1795. The first fundamental work was that by 
Ilensen in 1865 (31), and since then the most important 
papers are those by Hickson in 1880 (33), Carriére 
1885 (29), Patten 1886 (35), and Rawitz in 1888 (36). 
The structure of the retina was, however, still very 
uncertain, and this has been the chief feature of the 
works of Schreier 1896 (37), Hesse 1900 and 1907 (32), 
and Hyde 1905 (34), bringing the matter up to date. 
The difficulty of making satisfactory preparations, and 
the frequency of artifacts caused by fixation and further 
treatment, has been the cause of much confusion. 
The mantle, as previously described, has a margin 
bearing the characteristic lamellibranch structures (see 
fig. 4), There are three folds, on the outer of which are 
