66 



two are close together at the posterior margin of the foot; they project 

 backwards and are usually slightly longer than the anterior tentacles. 

 The position of these tentacles is indicated in Fig. 1. The anterior pores 

 are situated in the groove just posterior to the bases of the anterior 

 pedal tentacles ; the posterior pores are on the inside of the bases of the 

 posterior tentacles. In many cases there are two projecting papillae on 

 the inside of the base of the posterior tentacles, and the pores are near 

 the apices of these papillae. Sometimes the two posterior pores are so 

 close together that the two jets of water merge into one, and it appears 

 as if there were only one pore. These pores are not visible from the 

 exterior, even when examined with a lens, and are only seen when water 



is artificially injected through them. 

 The quantity of water which is 

 ejected by the animal often equals 

 as much as two to three centimetres. 

 Owingto the highly contractile 

 foot of these animals, it was very 

 difficult to obtain them killed in 

 the fully expanded state for section 

 cutting. The best expanded speci- 

 mens were obtained by use of coca- 

 ine, added gradually until the ani- 

 mals were fully narcotised, and then 

 placing in corrosive sublimate. The 

 sections were cut by the parrafin 

 method, and haematoxylin used as 

 the stain. The first series of sec- 

 tions of the anterior tentacular re- 

 gions of the foot, cut in transverse. 



Fig. 1. Ventral view of animal showing horizontal and vertical planes, 



position of the pedal tentacles on the foot, i ■■ • n r 14. • i 



T,,T.2^ 73, T,, pedal tentacles; SH, shell; Showed m all cases a slight mden- 



SI, siphon; OH, oval hood; PG, pedal tation of the ectoderm at the point 



gland : F, foot. ^^^^^ -^ ^^^ expected that the pore 



would be situated, but in no case was there a definite break in the epi- 

 thelium to show communication with the interior of the foot. It was there- 

 fore concluded that the muscular contraction of the foot had been too 

 great, and that the pores had become closed up. This conclusion was ren- 

 dered more likely by the fact that in no cases had the animals when dead 

 shown the full expansion of the foot. For this reason, before cutting 

 the next series of sections, an injection was made into the anterior 

 region of the foot. This was found to issue at the two posterior pores 

 at the inner base of the two posterior tentacles. Again an injection w^as 



