94 
REPORT— 1847. 
to have beea flattened against the discs that dosed the orifices of the peK 
foratious in the shell. Indeed in some instances these discs have remained 
adherent to them, when the shell-membranes were tom asunder; and are 
seen edgeways, as in fig. a. There can be no <loubt, therefore, that these 
membranous caca occupied, in the living aninml, the perforations already 
described as jieuetrating the shell from one surface to the otlicr. Thi* »ill 
be still more evident on reforixiice to fig. 39 of my former report; iu ffhici 
it will be seen bow exactly tiie sliapc of the caeca coirespotids with that of 
the perforations, when the latt^u' arc laid 0 |>eii leogtliways by a section of 
the shell perpendicular to its surface. The lower margin of that figure cor* 
r^ponds with tiie outer surface of the shell, and the diameter of the perfota. 
tions is seen to be there greatly increased. W’itli regard to the office of 
^ese cjEca, hou'ever, 1 am unable as yet to give any distinct explanation. 
Their contents are of a brown granular character, in which I have 
nis^ distinct ci-lla (fig. t), such as are to be mot with in the tubuii and 
iollicles of ordinary glantls; and their whole aspect satisfies me that they 
must be regarded as possessing agiandiilar character. I have not beenablei 
liowever, to discover the nature or destliiution of tlieir secretion *. The in* 
teriial orifices of the perforations olrviously constitute the outlets of the 
cffica; but tliere does nut appear to he any system of tubes or canals for cob 
loctmg the matters poured out from them, each ctecura having its distinct 
and independent txjrmimition on thn internal surface of the »he\L Although 
the unusual degree of mihosion between tlio mantle and the shells of Tere‘ 
Oratulw, first noticed by Professor Owen, formmly led me to suspect that the 
mantle might send prolongations into the perforations of the shell, lhavo not 
beenable to discover any vestige of such. On fi.e contrary', it has appeared to 
me la the umntle, which is a nearly homogeneous ntoiubrane where not 
ti-aversed by vessels, is simjdy applied to the internal orifices of the c®ca, 
Id continued over them ; no trace of any connection with them bring visi- 
bJe when it js detached from the shell. I may mention, liowevor, that I have 
nv .r ^ of Urn mantiH in contact with the ahclJ to he scatftred 
with minute cells corresponding in size and aspect with those con¬ 
tained in the cw^ tubes (fig. 4, a). 
pliysiolagical purpose of this curious structure, tlicrefore, is at 
piesent a mystery; but there can be little doubt thatit isa very important one 
vipnt Ubimal, when we see the shell thus rendered subser- 
evidpntlv protection of these cmcal appendages. And there is 
rations in rl>/. ^dr regarding the presence or absence of the perfo* 
trenus ® of greater value in the subdivifiou of the 
bv tliP *** ***“" thase more trivial judications fiiruished 
wUh thr^tnU eonlormation of tlm shell, which seem to have little to do 
with the structure or cecowomy of its inliabitant. I aai verv happy to find 
13racEZT\V°"M''^'-‘"“".‘•■“"'J' “■ th6daZificS»ffc 
absencc^of i has laid great stress ou the preseuM or 
rived from th Perforations, us exactly corresponding with characters de- 
rmUe cX. i ® arcaf. And I am 
(throuLdi ^rn^ td accept Ins correction of an error into which I had fallen 
I ougU an accidentol disarrangement of luy sections) in the classification 
opportunity of exomining* 
cimens preserved in spirit. * ” a betleridcs of thefonuer than is i)ossible from sj)*- 
los^calloUty^v^L ii.‘p! >■« the Joiimid of the Geo- 
