20 WALTER K. FISHER, 



to appear, so that all trace of a lumen is early lost. But potentially 

 the coelom is present. 



Circulatory System. 



The reader is referred to the diagram of the circulation of Lottia 

 gigantea, appended at the end of this account. A careful examination 

 of this chart will place the main features of the circulation in mind, 

 so that the following description will be easily understood. 



In common with other Docoglossa the pericardium of Lottia 

 gigantea is situated on the left anterior part of the dorsal side of 

 the body. It is roughly triangular in outline and rather shallow dorso- 

 ventrally (Fig. 22 Per). Its left side is formed by the anterior portion 

 of the left limb of the U- or horseshoe-shaped shell muscle. The 

 right side (occupied by the auricle) abuts against the mantle-hood 

 and mantle cavity. The posterior or remaining side of the triangle 

 lies against and over a portion of the gonad (Fig. 20). Immediately 

 beneath the pericardium is the gonad (Fig. 1). 



Fig. H. Conventionalized cross-section through middle of animal to show relations 

 of arterial and venous circulation in foot and mantle. The sinuses of the foot are in 

 white, the arteries in black. A. Sp arterial sinuses of mantle, C. P. S circumpallial 

 sinus, F foot, M. V mantle veins, Med. S median sinus, Neu neural arteries, Ped. A pedal 

 arteries, Ped. V pedal sinuses. 



The heart consists of an auricle and ventricle. The former oc- 

 cupies the right side of the pericardium. Anteriorly its walls are 

 produced to meet the pallial sinus. They join the walls of the sinus 

 near the outer edge of the spindle muscle on all sides except the 

 right, where the blood must enter from the pallial hood (Fig. 24). 



