Laguna Q9arine Laboratory 87 



length of ventral arm 135 imn. ; length of tentacle 327 mm. ; length of 

 tentacle club 73 mm. 



Polypus bimaculatus (Verrill 1883) 

 (Figures 47 and 48) 



A specimen of this species (S. S. B. No. 324) was taken by Mr. 

 Metz in one of the lower tide-pools at Laguua, and numerous other 

 specimens by other members of the laboratory. It is the common 

 shore "octopus" of Southern California and has been previously 

 reported from White 's Point, San Pedro and San Diego. The large, 

 eye-like, lateral markings near the base of each arm of the third pair 

 constitute its most conspicuous specific character. In the present 

 specimen the usual bluish ring* surrounding the central spot is 

 obscured or absent. 



A microscopic examination of a portion of the integument in the 

 neighborhood of these markings shows that the outer ring of the 

 oculation owes its pale color chietly to a diminution in the number of 

 cliromatophores over this area.f Similarly the dark center is due 

 to a great and sudden increase in their frequency. The exact number 

 is somewhat variable, but a given space in the dark center appears 

 to contain fully twice as many as an equal area in the paler border. 



Even when expanded, all the cliromatophores are excessively 

 small. In the present material the dimensions of one of these organs 

 is .09 x.l 6 mm. expanded, and .04 x .06 mm. in diameter contracted. 

 Their detailed structure is correspondingly difficult to make out. 



The illustrations accompanying this paper were prepared by Mr. 

 John Howard Paine of Stanford University, Mr. Metz and Miss 

 Mabel Guernsey. 



'Berry, Univ. Calif. Publ. Zool., vol. IS, p. 30.', 1911. 



(Whether the pigment within the chromatophores themselves is likewise differen- 

 tiated either in color or qmmtity, cannot of course he determined without examining fresh 

 material. 



