326 



Gilmari A . Drew 



ings nor collaterals in the pedal ganglia but are continued to the 

 cerebral ganglia. 



7 Impulses may pass in both directions through any of the 

 commissures and connectives. 



8 Stimulation may cause impulses to be sent by roundabout 

 connections when the usual connections are destroyed, but the 

 stimulation must be of considerable duration and the result is 

 often considerably delayed. 



University of Maine 

 January 7, 1908 



EXPLANATION OF PLATE 



The anatomy of Etisis directus, Con. 



Fig. I A specimen as seen from the right side with both valves of the shell, the right lobe of the 

 mantle, the right labial palps and the right gills removed. Represented with the siphons and collar 

 extended and the foot slightly protruded. Avery common position. Drawn from the study of dissec- 

 tions and serial sections and enlarged to about one and one-third natural size. 



Fig. 2 A specimen as seen from the ventral surface with the mantle margins cut and the shell valves 

 wide apart, and the foot forced posteriorly and to the right side of the animal. The inner lamellae of the 

 inner gills have been separated and pushed to the sides. The ganglia and nerves in this figure have 

 unintentionally been made a little too large. Drawn from dissections with a few details added from the 

 study of serial sections. Enlarged to about one and one-half natural size. 



aa anterior adductor muscle h heart 



aan anterior adductor muscle nerve Ip labial palp 



af anterior foot muscle Ipn labial palp nerve 



ajn anterior foot muscle nerve m mouth 



apn anterior pallial nerve pa posterior adductor muscle 



hn branchial nerve pan posterior adductor muscle nerve 



hs branchial siphon pfm posterior foot muscle 



c collar pg pedal ganglion 



cc cerebral commissure pn pedal nerves 



eg cerebral ganglion ppn posterior pallial nerve 



cpc cerebro-pedal connective r rectum 



cpn circum-pallial nerve 5 crystalline style 



.cs cloacal siphon it stomach 



cvc cerebro-visceral connective vg visceral ganglion 



/ foot vm visceral mass 



g gill vo ventral mantle opening 



