495 



the ventral side of the inhalent siphon remains distinct even in adult 

 specimens. 



The tentacles that fringe the postero-ventral margins of the mantle, 

 are each supplied with longitudinal and transverse strands of muscle- 

 fibers, and with several blood-spaces. Their nervous supply is appar- 

 ently from branches of the posterior pallial nerves. They are preceded 

 in development by sense papillae, such as has been described by 

 Flemming (1), as "Pinselzellen". Growth takes place at the bases of 

 these papillae, and they are carried out at the tips of the tentacles. 

 As growth continues, other papillae appear on the sides of the tentacles, 

 and the original ones may shift their positions. 



afm 



Fig. 1. Adult specimen of Yoldia limatula, represented as seen from the right side. 

 Reconstructed to show internal organs. Fully grown specimens may be 6 cm long. 

 aa anterior adductor muscle, afm anterior foot - muscles, bg byssal gland, eg cerebral 

 ganglion, es exhalent siphon. / foot, g gill, h heart, int intestine, is inhalent siphon. 

 Ip labial palp, ot otocyst. pa posterior adductor muscle, pap palp-appendage, pe posterior 

 expansion of the margin of the mantle, pfm posterior foot-muscle, pg pedal ganglion, st 

 siphonal tentacle, sto stomach, vg visceral ganglion. 



The unpaired siphonal tentacle, Fig. 1 st, is very long and slender, 

 and gradually tapers to its free extremity. When extended, it gen- 

 erally lies in loops on the surface of the mud in which the animal 

 lives. It is attached to the mantle near the ventral border of the 

 base of the siphons, on either the right or the left side. Throughout 

 its length its surface is set with small conical papillae, such as have 

 been mentioned in connection with the ordinary tentacles. Beneath 

 the layer of epithelium run strands of longitudinal muscle-fibers im- 



33* 



