F. CEPHALOPODA : SUMMARY OF IMPORTANT FACTS. 395 



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

 (>?((«;(/«,* the giant squid (p. 384). Myopsida. Oviduct single (left) ; cornea 

 unpei-forated. Loliijo* common squid ; Rossia*; Sepia, cuttle fish, fur- 

 nishing the ' oiittle 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, 



,^r^S?'-"% 



Fig. 388. — Argonauta argo, paper sailor, female. (After Rymer Jones.) 



OCTOPODID^. Octopus * (fig. 397), AUoposus* Argonautid^, female with 

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

 avf/o, paper nautilus. In the Argonautidie and Philonexid^e the heoto- 

 cotylus separates of itself. 



Summary of Important Facts. 



1. The MOLLUSCA are parencliymatous animals with re- 

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



2. Tlie head bears eyes and tentack'S. 



3. The foot is an unpaired muscuhir 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 groujis. 



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

 system. 



