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On 
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DR. H. LYSTER JAMESON ON 
(17) EXPLANATION OF THE PLATES 
(The magnifications quoted are only approximate.) 
PruatE XXXIII. 
Fig. 1. Cestode larva (Tylocephalum ludificans or T. minus) in the act of migrating 
through the tissues of Margaritifera v ulgaris. Drawn trom one of Prof. 
Herdman’s shdes. The larva measured "12 mm. pa., parenchymatous 
subepidermal tissue ; c.¢.f., connective-tissue fibres. 
Fig, 2. Small larva, Tylocephalum minus, measuring ‘O8 mm., in the muscular 
tissue of the mantle of MZ. vulgaris, without a surrounding connective- 
tissue cyst. From one of Prof. Herdman’s slides. m.f., muscle-fibres in 
cross-section ; ep., epidermis. 
Fig. 3. Part of the fibrous cyst surrounding an example of the sinaller parasi.e 
(Tylocephalum minus). In this case the parasite measured *O8 mm. in 
diameter. J.¢., liver-tubules; 7./., inner, highly nucleated layer of the cyst. 
x 800. 
Fig. 4. Margaritifera vulgaris. Epithelial cells from the muscle-attachinent, 
showing the connection between the cells and the muscle-fibres. 
x 1000. 
Fig. 4a. Margaritifera vulgaris. Muscle-attachment epithelium, showing cells 
drawn out in fixation, and connective-tissue elements between their bases. 
X 1200. 
Proare XXXIV. 
Fig. 5. Mytilus edulis. Section through the posterior adductor muscle-insertion 
and decalcitied hy postracum. mus., muscle-fibres; hy., hypostracum, 
which remains adherent to the muscle-attachment epithelium, ep. ; 
hy.’, segment of hypostracum, corresponding to single epidermal cell; 
nac., nacreous layers of the shell, which have torn away from the hypo- 
stracum ; c¢., connective-tissue tibres, joining the muscle-fibres to the 
attachment- epithelium. Preparation XXXIX. X 500. 
Fig. 6. Margaritifera vulgaris, Persian Gulf. The part represented at A in 
text-figure 35, showing the point of origin of a new lip-lappet of the shell. 
1., 1.’, two suce cessively formed lappets. or marginal processes; pr., pr.’, 
prisms of same; s.pr., s.pr.’, couchyolin-septa of the prisms; b.m.pr., 
conchyolin basal membrane of the prismatic substance of the first lappet ; 
per., periostracum of the second lappet, which appears to be nothing 
more than the outer conchyolin-membrane of the prismatic substance ; 
point at which the second lappet arises from ‘the first, the peri- 
ostracum of the seeond lappet being continuous with the basal 
membrane of the first; y, irregular prismatic substance secreted at the 
junction of the two lappets. Preparation X. x 300. 
Fig. 6a. Margaritifera vulgaris, Persian Gulf. Decalcitied shell showing junction 
between prismatic substance and nacre. pr., prisms; sep., conchyolin- 
septa between same; sep.’, the same in surface view; anw., annular 
thickenings of the septa; p7.b., basal conchyolin of the prismatic layer ; 
con., connecting layer of alveolar conchy olin between the prisms and the 
nacre; 2ac., nacre. Prepavation XI. xX 400. 
Fig. 7. Margaritifer a vulgaris, Persian Gulf. “ Lingah Sheli” from London 
market. Section ground from an old heavy shell. Portion of the adductor- 
scar, showing the hypostracum, /iy., covered over in the direction of the 
umbo by nacre, nae.’ ; nae., nacre underlying the muscle-scar, and secreted 
before the muscle-attachment had moved to this place; hy.’, hy.'', extensions 
of the hypostracum interstratified with nacre. Preparatica LXXYV. 
X 120. 
Puare XXXV. 
Fig. 8. Muscle-pearl and hypostracum “cyst,” from the insertion of the posterior 
pedal levator muscle of Margaritifera vulgaris. From a Ceylon specimen 
given to me by Professor Herdman. The pearl is enclosed in a sac (which 
has been ruptured by gas-bubbles in the decalcifying process), consisting 
mainly of ordinary shell- secreting epithelium, bat lined at one pole with 
muscle-attachment epithelium (m.ep.’). Opposite the ordinary epitheliam 
L94] 
