352 DR. H. LYSTER JAMESON ON 



(17) EXPLANATION OF THE PLATES. 

 (The magnifications quoted are only approximate.) 



Plate XXXIII. 



Fig. 1. Cestocle larva {Tylocephalum ludificans or T. minus) in the act of migrating 

 through the tissues of Margaricifera vulgaris. JJrawn from one of Prof. 

 Herdman's slides. The larva measured •12 mm. pa., parenchymatous 

 subepidermal tissue ; c.t.f., connective-tissue fibres. 



Fig. 2. Small larva, Ti/locephalum mitms, measuring '08 mm., in the muscular 

 tissue of the mantle of M. 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 smaller parasite 

 {Tj/locepJialum minus). In this case the parasite measured "08 nmi. in 

 diameter, l.f., liver-tubules ; i.l., inner, higlily nucleated layer of the 03 st. 

 X800. 



Fig. 4. Ilargaritifera vulgaris. Epithelial cells from the muscle-attachment, 

 showing the coimection between the cells and the muscle- fibres. 

 X 1000. 



Fig. 4 a. Slargaritifera vulgaris. Muscle-attachment epithelium, showing cells 

 drawn out in fixation, and connective-tissue elements between their bases. 

 X 1200. 



Plate XXXIV. 



Fig. 5. Mytilvs edulis. Section through the posterior adductor muscle-insertion 

 and decalcified liypostracum. mus., muscle-fibres; %., hypostracuni, 

 which remains adherent to the muscle-attachment • epithelium, ep. ; 

 hi/.', segment of hypostracum, corresponding to single epidermal cell ; 

 liac, nacreous layers of the shell, which have torn away from the hypo- 

 stracum ; ct., connective-tissue fibres, 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. 

 I., I.', two successively formed lappets or marginal processes; pr., pr.', 

 prisms of same; s.pr., s.pr.', conchyolin-septa of the prisms; h.m.pr., 

 conchyolin basal membrane of the prismatic substance of the first lappet ; 

 per., periostracirm of the second lappet, which appears to be nothing 

 more than the o-.iter conchyolin-membrane of the prismatic substance ; 

 X, 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. 6 a. Margaritifera vulgaris, Persian Gulf. Decalcified shell showing junction 

 between prismatic substance and nacre, pr., prisms ; sep., conchyolin- 

 septa between same ; sep.', the same in surface view ; anu., annular 

 thickenings of the septa; pr.b., basal conchyolin of the prismatic layer ; 

 con., connecting layer of alveolar conchyolin between the prisms and the 

 nacre ; wac, nacre. Preparation XI. X 400. 



Fig. 7. Margaritifera vulgaris, Persian Gulf. " Lin gab Shell" from London 

 market. Section ground from an old heavy shell. Poi-tion of the adductor- 

 scar, showing the" hypostracum, hy., covered over in the direction of the 

 umbo by nacre, uac' ; nac, nacre underlying the muscle-scar, and secreted 

 before the muscle-attachment had moved to this place ; liy.', hy.", extensions 

 of the hypostracum interstratified . with nacre. Preparation LXXV. 

 X 120. 



Plate XXXV. 



Fio-. 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, but lined at one pole with 

 muscle-attachment epithelium {m.ep.'). Opposite the ordinary epithelium 



