Laguna Warine Laboratory 87 
length of ventral arm 135 mm.; length of tentacle 327 mm.; length of 
tentacle club 73 mim. 
Polypus bimaculatus (Verrill 1883) 
(Figures 47 and 48) 
A specimen of this species (S. 8. B. No. 324) was taken by Mr. 
Metz in one of the lower tide-pools at Laguna, 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 
obseured 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 chiefly to a diminution in the number of 
chromatophores over this area.t 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 chromatophores are excessively 
small. In the present material the dimensions of one of these organs 
is .09 x .16 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. 18, p. 302, 1911. 
;Whether the pigment within the chromatophores themselves is likewise differen- 
tiated either in color or quantity, cannot of course be determined without examining fresh 
material. 
