ig2 



ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA 



Ascidians have a cellulose test, not a calcareous shell. The larval 

 conditions are totally distinct. 



If, however, all Cephalous Mollusks, i.e., all Cephalopoda, Gastero- 

 poda, and Lamellibranchiata, be only modifications by excess or 

 defect of the parts of a definite archetype, then, I think, it follows as a 

 necessar)' consequence that no anamorphism takes place in this group. 

 There is no progression from a lower to a higher type, but merely a 

 more or less complete evolution of one type. 



It may indeed be a matter of very grave consideration whether 

 true anamorphosis ever occurs in the whole animal kingdom. If it do, 

 then the doctrine that every natural group is organized after a definite 

 archetype, a doctrine which seems to me as important for zoology as 

 the theory of definite proportions for chemistr)', must be given up. 



DESCRIPTION OF THE PLATES. 

 In all the Plates the same letters refer to the same parts. 



a. Anus. 



d. Buccal mass. 



c. Contractile sac. 



d. Subspiral ciliated t)and. 

 e/>. Epipodium. 



y. Salivary gland. 



g. Tentacles. 



/i. Head. 



I. Eye or optic nerve. 



J. Auditory vesicle or nerve. 



/c. Stomach. 



/:'. Pyloric co;cum. 



/. Liver. 



m. Mantle. 



alt. Metapodium. 



HIS. Mesopodium. 



?/. Branchiae. 



1- 



It . 



V. 





Ovary. 



Penis. 



Propodium . 



Abdomen. 



Post-abdomen. 



Vesicula seminalis. 



Testis. 



Auricle. 



Venous canal. 



Ventricle. 



Aorta. 



Recurrent artery. 



Cerebral ganglia. 



Pedal ganglia. 



Pedal artery. 



Parieto-splanchnic gangli; 



8. Buccal ganglia or nerves. 



y. Crystalline style. 



A. Its sheath. 



S. Accessory cartilages of the buccal mass. 



fl. Tongue plate. 



f). Elastic plate. 



jx. Muscles. 



Fig. I 

 Fig. 2 



Fig. 3 

 Fig. 4, 

 Kg. 5 



Firoldides Desinarestii. 

 Firoldides Desniarestii. 

 Firoldides Desinarestii. 

 Penis of the male. 

 Egg-tube. 



PL. H. [Plate 17] 



(Magnified.) Male. 



Female. Posterior extremity from the left side. 



Female. Posterior extremity from the right side. 



