MOLLUSCA : CEPHALOPODA. 



273 



fluid to the female. The mode in which this is effected varies 

 in different species. Thus, in the male Octopus (the Poulpe) 

 the third right arm is primitively developed in a cyst, which 

 ultimately ruptures and liberates the metamorphosed arm, 

 which then appears to be of greater size than the correspond- 

 ing arm on the left side, and to terminate in an oval plate 

 (Jig. 83). To this terminal plate the spermatophore is probably 

 transmitted, but the arm itself remains permanently attached 

 to the animal. In Tremoctopus the third right arm of the 

 male is ' hectocotylised,' and is converted into a vermiform 

 body, with two rows of ventral suckers, and an oval appen- 

 dage or sac behind, which contains spermatozoa. Besides the 

 suckers, the anterior part of the back is fringed with a number 

 of so-called ' branchial ' filaments. 



In the Argonaut the male is not more than an inch in length, 

 is devoid of a shell, and has its third left arm hectocotylised. 



"a 



Fig. 83. Octopus carena (male), showing cyst in place of the third arm. 2. Ventral 

 side of an individual more developed, with the hectocotylus (a), (After 

 Woodward.) 



This arm is developed in a cyst, which is ruptured by the 

 movements of the * hectocotylus,' which then appears as a 



VOL. I. T 



