in 



Guide to the Imertebrata. 



Belem- a single pair of comb-like gills. The oviducts are sometimes 



__P^ paired (right and left), sometimes only one is developed. A 



VII. horny or calcareous internal shell is developed in most of them, 



enclosed in a sac formed by the mantle ; in the Octopoda the 



shell is not developed, save in Argonauta, the female of which 



secretes a shell (Fig. 35). 



The eyes are very highly-developed organs, with a refractive 

 lens, cornea, and eyelids. They are the most striking organs in 



Fig. 28. — Belemnoteuthis anttqua, 

 Cuunington. Oxfordian : 

 Christian Malford, Wilts. 

 A, booklets on arms ; m, 

 mantle ; other letters as in 

 Fi-. 31. 



Fig. 29. — Diagrammatic restoration of the 

 animal and shell of Belemnite (after 

 D'Orbigny). 



these creatures, being both large and brilliant, and well express 

 the keen activity and alertness for which the majority of this 

 wonderful group is conspicuous. 



All the Dibranchiata secrete an inky fluid, and possess an 

 "ink-bag," having a tough and fibrous structure, with a thin, 



