The Circulatory System of Laila Cockerelli 
MABEL GUERNSEY 
Laila cockerelli is the single species of a genus of Doridide 
described by MacFarland in 1905. Since it is very abundant at 
Laguna Beach, I undertook a study of the anatomy, of which this 
paper, on the circulatory system, is a part. Most of the speci- 
mens with which I worked were fixed with chrome-acetic acid for 
sectioning, as the small size of the animal, the length of which 
ranged from 10 to 15 mm., made dissection unsatisfactory. 
The only part of the circulatory system which it was con- 
venient to dissect was the heart. This is situated close beneath 
the upper body wall, just anterior to the branchie, and in the 
living animal its pulsations may sometimes be seen through the 
skin. The heart consists of an oval or nearly circular, flattish 
ventricle and a very large, thin-walled auricle, both enclosed in 
a delicate pericardium. The ventricle contains many interlacing 
muscle-fibres, which form a network between the walls, so that 
the contracted ventricle appears as a thick mass of muscle-fibres. 
Between the auricle and ventricle, circularly placed muscle-fibres 
form a valve. The walls of the auricle are extremely thin, con- 
sisting of a delicate sheet of connective tissue, strengthened by a 
very few bands of muscle-fibres. The enclosing pericardium is 
thin, but thicker than the wall of the auricle, and contains numer- 
ous nuclei. 
Since dissection or injection was very difficult, the course of 
the circulation was determined by making a graphic reconstruc- 
tion from serial sections. The drawing was from a reduction of 
this reconstruction. The reconstruction of the arterial circula- 
tion was made from a smaller animal than that of the venous 
circulation, and is consequently drawn to a different scale. This 
was done because the arterial system was imperfectly preserved 
in the specimen that showed the venous system to best advantage. 
No attempt was made to reconstruct the pedal sinuses, which are 
a complex, interlacing mass, reminding one of the interstices of 
a sponge. The arterial circulation was especially difficult to 
