The Circulatory System of Laila Cockerelli 



MABEL GUERNSEY 



Laila cockerelli is the single species of a genus of Dorididse 

 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 uusatisfactorj'. 



The only i)art 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 branchiae, and in the 

 living animal its pulsations may sometimes be seen through the 

 skin. The heart consists of an oval or nearly circular, flatfish 

 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 mi;scle-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 artei-ial circulation was especially difficult to 



