THE TWO-GILLED GROUP 



3301 



free and independent life for a considerable period. The eggs are small, numerous, 

 and connected by a network of filaments. They are deposited far within 

 the shell toward the convoluted portion, and are practically in contact with the 

 posterior part of the body of the parent. The shell therefore serves, not only as a 

 retreat for the argonaut herself, but also as a nest for her eggs, and possibly as a nurs- 

 ery for the young. Very little is known in regard to the food of the argonaut. As 

 its habits are very similar to those of the octopus, it seems probable that it may feed 

 upon mollusks and crustaceans, which it might capture when crawling at the bottom 



A. MALE ARGONAUT (twice natural size), WITH HECTOCOTYLUS INCLOSED IN THE SACK; B. 



MALE ARGONAUT,. WITH HECTOCOTYI.US FURTHER DEVELOPED. 



of the sea. A captive specimen was fed with small live fish, which it ate with 

 avidity. About eight species are recognized, which have a world-wide distribution, 

 occurring in all tropical and warm latitudes. The shells of the different species are 

 all of a white color, and exhibit two distinct types of surface ornamentation, the one 

 consisting of simple, smooth, radiating wavy ribs, the other in which these ribs are 

 more or less broken up into nodules or tubercles. Argonauta /nans is the typical 

 species of the former group, and A. namcula and A. tuberculata represent the 

 latter. 



SUBORDER Decapoda 



The Decapods form the second division of the two-gilled order, and differ from 

 the Octopods, as the name implies, by the possession of ten, instead of eight, arms. 

 The two additional arms differ from the rest in their greater length, and in having 

 suckers only at the extremity. They are frequently completely retractile within 

 pouches, and are used as prehensile organs in the capture of their prey. All deca- 



