☞ They have, around the front of the head, a group of elongated muscular arms, which are usually furnished with prehensile suckers or hooks. The head is highly developed, with large, well organized eyes and ears, and usually with a cartilaginous brain case. The higher forms, as the cuttlefishes, squids, and octopi, swim rapidly by ejecting a jet of water from the tubular siphon beneath the head. They have a pair of powerful horny jaws shaped like a parrot’s beak, and a bag of inklike fluid which they can eject from the siphon, thus clouding the water in order to escape from their enemies. They are divided into two orders, the , having two gills and eight or ten sucker-bearing arms, and the , with four gills and numerous arms without suckers. The latter are all extinct except the . See

Octopus

,

Squid

,

Nautilus

.