V. CEPHALOPODA : SUMMARY OF IMPORTANT FACTS. 395 



and two oviducts. Ommastrephes common in New England ; Archi- 

 teuthis*tt\e giant squid (p. 384). MYOPSIDA. Oviduct single (left) ; cornea 

 unperforated. Loligo* common squid; Rossia*; Sepia, cuttle fish, fur- 

 nishing the ' cuttle bone ' once used in medicine, now fed to cage birds, 

 and the pigment sepia. 



Sub Order II. OCTOPODA. Eight arms webbed at their base; shell 

 very rudimentary, sometimes fragmentary or wanting ; oviducts paired, 



FIG. 398. Argonauta argo, paper sailor, female. (After Rymer Jones.) 



OCTOPODID^E, Octopus * (fig. 397), Alloposus.* ARGONAUTID^E, female with 

 boat-like shell (fig. 398), males much smaller and without shell. Argonauta 

 argo, paper nautilus. In the Argonautidse and PHILONEXID.E the hecto- 

 cotylus separates of itself. 



Summary of Important Facts. 



1. The MOLLUSC A are parenchymatous animals with re- 

 duced coelom. They consist of head, visceral sac, mantle, and foot. 



2. The head bears eyes and tentacles. 



3. The foot is an unpaired muscular mass used in locomotion. 



4. The mantle bounds the mantle cavity which is connected 

 with respiration; it either functions as a lung or covers the gills 

 (ctenidia). It secretes the shell from its outer surface. 



5. Foot, head, mantle, and with the latter the shell, may be 

 lost in many groups. 



6. The molluscs, without exception, agree in the nervous 

 system. 



