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Show 1900.] A RARE CUTTLEFISH. 995 three pairs, near the base of which they are each about 1 inch broad. The muscular folds that connect the bases of the arms externally are as follows : - A fold or web connects the bases of the ventral and ventro-lateral arms, forming the outer wall of a hollow, about 2 inches in depth, within which the tentacle arises. This web is attached to the outer or aboral surface of the ventro-lateral arm, which it crosses to form a similar narrow web or festoon extending to the postero-lateral arm. In the case of the ventral arm it is continued all the way up the dorsal margin in the form of a deep thin frill or keel lying not far distant from the smaller web adjacent to the suckers : a little way from the base this keel is about lf inches broad. Corresponding to it on the opposite or ventral margin is a very much narrower keel, which appears, however, only to commence about 4 inches from the base of the arm; above this point it quickly grows to about half an inch in breadth, and extends, slowly narrowing, to about halfway up the arm. In the case of the dorsal arm, there is a very rudimentary keel on the outer side, which does not pass over to join the dorsolateral arm. The dorso-lateral arm has a well-developed keel on the ventral side, which joins the ventro-lateral arm. There is yet another series of folds or membranes connected with the bases of the arms, external to the circumoral membrane. Firstly, a muscular fold runs from the internal aspect of the ventral arm to its fellow on the one hand and to the oral aspect of the ventro-lateral arm on the other, marking off here the oral boundary of a cavity or pouch, which is separated by another similar fold from the cavity out of which the tentacle arises, but out of which comes to the tentacle a special fold of membrane within which appears to lie the tentacular nerve. In Ommastrephes the inner or the above muscular folds appears to be absent, the homologous pouch being bounded outwardly by the wall of the tentacular sac and inwardly by the buccal membrane. Another muscular fold, belonging apparently to the same series, unites the inner aspects of the 2nd and 3rd, and 3rd and 4th arms respectively, so that between the bases of each of these pairs of arms is a slight pouched cavity somewhat similar to that from which, between the 1st and 2nd, the tentacle grows. The suckers are in two rows, and commence on the dorsal arm about 2 inches, and in the others about 3 inches from the base. In the two rows the suckers are obliquely opposite one another, and their bases near the base of the ventral arm are about one inch apart in the case of two opposite suckers, and a little more in the case of two contiguous ones on the same side. There are on the ventral arm about fifty distinct pairs, beyond which for about 2 inches at the distal end of the arm the paired arrangement is not clearly maintained. The suckers on the major portion of the ventral arm are about T % inch diam., those on the other arms being perceptibly larger, about f inch diam., towards the middle of each arm. The ventro-lateral arm has about 29 pairs of suckers, and then for PROC. ZOOL. Soc-1900, No. LXV. 65 |
