EXPLANATION OF PLATE IIL 



Shell-glands of the Viviparidae. 



Fig. I.— Vertical section through the roof of the lower part of 

 the branchial chamber just above the mouth in 

 Lecythoconcha Iccylhis (Benson) at birth, X 75. Stained 

 with Delafield's haematoxylin. 



,, 2. — Part of the same section ( X 275), including two ducts 

 of the calciferous gland. 



,, 3. — Vertical section through the free edge of the mantle in 

 approximately the same region in an adult of the 

 same species. The mantle was not much contracted 

 and the animal was still growing. vStained with eosin 

 and haematoxyUn. 



,, 4. — Vertical section of the mantle in the same region in 

 another adult individual of the same species The 

 whole animal was highly contracted and was evidently 

 undergoing a period of arrested growth. The connec- 

 tive tissue of the mantle was markedly degenerate in 

 places owing to the presence of encysted trematode 

 parasites (Urogoniiiius). Stained with Delafield's 

 haematoxj'lin. 



,, 5. — Vertical section through the same region in the adult of 

 Vivipara oxytropis (Benson) in a period of arrested 

 growth. Stained with borax carmine. 



Explanation of Lettering. 



b. s., blood- sinus ; c, calcareous concretion ; c.e., ciliated 

 eipthelium ; m., external retractor muscle; m'., sphincter of 

 mantle ; m"., muscular network ; m. p., peripheral marginal pro- 

 cess ; p. g., periostracal gland ; p. g. d., duct of periostracal 

 gland; s. §■., calciferous gland; s. g. rf. , temporary duct of calci- 

 ferous gland ; s.p. gr., supramarginal groove. 



