ï 9 i6.] 



Fauna of the Chilka Lake : Mollusca Gastropoda, etc. 



369 



Fig. 2. — Solen ? fonesi, D tinker. 



Transverse section of the wall of the siphon. 



1. outer epithelial lining; 2. outer layer of connective 

 tissue; 3. longitudinal layer oE muscles; 4. transverse layer 

 of muscles ; 5. longitudinal layer of muscles ; 6. epithelial 

 lining of the inhalent tube of the siphon ; 7. part of transverse 

 partition. 



The wall consists of the following layers : — 



(1) An outer layer of columnar cells situated on a distinct basement membrane. 



(2) A thick layer of connective tissue with many elastic fibres and connective 



tissue corpuscles. The 

 fibres are mostly arranged 

 circularly and radially in 

 narrow bundles at regular 

 intervals. They are conti- 

 nued into the next layer. 



(3) A thick longitudinal layer of 



muscles fibres grouped into 

 radial bundles by radial 

 and longitudinal partitions 

 of connective tissue which 

 extend from the second 

 layer to the next. The 

 muscular layer is divided 

 into an outer and an inner 

 portion by a thin circular 

 layer of connective tissue 

 fused with the radial ones at their points of crossing. This thin layer of 

 connective tissue is united on both sides by a thin layer of the same tissue, 

 which forms the middle of the thick transverse partition between the 

 inhalent and exhalent canals. At the 

 junction of the two lie two blood-sinuses, 

 one on either side. On either side of 

 this median layer lies a narrow longitu- 

 dinal layer of muscular tissue continu- 

 ous with the inner portion of the longi- 

 tudinal layer of muscular fibres in the 

 wall of the siphon. 



(4) A thin layer of connective tissue which is 



interrupted at the junction of the outer 



wall of the siphon with the transverse 



partition. In this layer and abutting 



on the next outer muscular layer are 



blood-sinuses and nerves disposed in the 



following manner : — The blood-sinuses 



are 4 in number — two lateral already 



referred to, and one in the mid-dorsal 



and one in the mid-ventral line. The nerves are 12 in number, three on 



each side of the inhalent and three on each side of the exhalent aperture. 



Fig. 3. — Solen ? fonesi, Dunker. 



Longitudinal section through wall of siphon 

 at junction of two contiguous segments. 



1. outer epithelial lining ; 2. outer layer 

 of connective tissue ; 3. longitudinal layer 

 of muscles ; 4. inner longitudinal layer of 

 muscles; 5. inner epithelial lining ; 6. radial 

 layer of muscles. 



