LOLIGO PEALII LESUEUR 233 



ventral axis as the longitudinal axis. To avoid confusion the 

 terms anterior and posterior, dorsal and ventral will be restricted 

 to their morphological meaning and will have the same value as 

 in other molluscs. On the other hand, the terms upper and lower, 

 fore and hind, left and right will be applied for the various re- 

 gions of the body in the natural position of the swimming animal. 

 External Features. The body of the squid is divided into 

 head, neck and trunk. The mouth is surrounded by ten arms 

 two of which differ from the rest and are called tentacles. It is 

 customary to count the arms beginning at the upper surface of 

 the head. The fourth or last pair of arms is below the mouth 

 and the tentacles are between the third and fourth pair. The 

 third pair of arms is the longest but still considerably shorter 

 than the tentacles. A muscular membrane attached to the base 

 of the arms extends from these to the mouth. Its peripheral 

 portion called the buccal membrane, possesses seven muscular 

 projections each bearing two rows of small suckers on the sur- 

 face facing the mouth. One of these projections is situated 

 in the plane of symmetry above the mouth, /. e., between the 

 first pair of arms. The inner part of the membrane, immedi- 

 ately surrounding the mouth, is called the peristomial membrane. 

 In the female there is a special horseshoe organ on the buccal 

 membrane in the median line below the mouth. This organ 

 serves for the attachment of spermatophores. The four pairs 

 of arms are sessile, gradually tapering toward the end and all 

 but the third pair are trapezoidal at base. They are provided 

 with inner and outer marginal membranes and two rows of suck- 

 ers. Each sucker is composed of a short pedicel and cup the edge 

 of which is strengthened by a serrated chitinous ring. The 

 central part of the base of the cup is formed by the piston which 

 is the end of the pedicel. The largest suckers are at the base 

 of each arm. The tentacles are retractile. They are composed of 

 a peduncle and a terminal club on which the suckers sit in four 

 rows; the largest suckers are in the middle of the club. The 

 peduncle of the tentacles sits in a sac formed by the outer 



