3 68 



Memoirs of the Indian Museum. 



[Voi,. V ; 



labial-palps of one side were then removed and the animal was examined under a 

 low power. The coils of the intestine, the ganglia, some of their commissures, and 

 the general outline of the kidneys were well made out by this method. 



(3) Lastly, a complete set of serial sections was cut by the paraffin method from 

 one end of the animal to the other, and stained as usual. The arrangement and the 

 relation of the various structures made out in the serial sections were compared with 

 the results obtained by other methods. 



I. MANTTvE-IvOBES. 



The anterior margins are thick and straight and run a little forward from above ; 

 they are separate from one another in their full lengths so as to leave an oval gap for 

 the foot. The separation extends beyond the antero-ventral corner for a short dis- 

 tance as a rounded notch. The ventral margins are united and thickened, although 

 less so than the free anterior borders. The posterior margins are thickened and 

 united to form a single siphon containing both the inhalent and exhalent canals. 



16 



Fig. 1. — Solen ? fonesi, Dunker. 



i. anterior adductor muscle ; 2. posterior adductor muscle ; 3. posterior retractor muscle ; 4. stomach; 5. liver; 

 6. intestine; 7. pyloric caecum; 8. rectum; 9. gill (inner); 10. heart; 11. kidney; 12. pedal sinus; 13. pedal 

 ganglion; 14, cerebral ganglion ; 15. visceral ganglion ; t6. remains of siphons after autotomy. 



II. Siphon. 



The siphon consists of the fused inhalent and exhalent canals. When complete 

 it consists of at least ten segments, each of which is wider at the base than at the apex. 

 Each segment is at its distal border fringed with small conical tentacles, about 20 in 

 number and arranged in a single row (see text-fig. 5, p. 354). When complete and fully 

 extended, the siphon reaches a length nearly equal to that of the animal in the shell. 

 When fully retracted and when a part has been thrown off the siphon lies very 

 slightly protruded from the posterior border of the mantle-lobes. In the retracted 

 state, the distal segment is less contracted than the others, forming a tumid rounded 

 border bounding the inhalent and exhalent apertures. The tentacles are retracted 

 and turned inwards towards the apertures. 



Minute structure (figs. 2, 3). — In a transverse section, the siphon consists of a 

 thick wall with a transverse band separating the apertures (text-fig. 2). 



