30 E. S. Morse—Classification of Mollusca 
tentacles surround the mouth only; the anus terminating out- 
side the lophophore. Witness in the highest order of Cephalo- 
s, the Dibranchiates, the sae as in Loligo (Series I, C), long 
and cylindrical, and in all cases mouth and anus opening ante- 
riorly; the arms surrounding the mouth only. Two rough 
diagrams, alike in form, but reversed in one case, would repre- 
sent each class as we have it here. In Brachiopoda (Series U, 
, L) the same. The relative diameters of the Monomyarians 
are unlike those of any other class, as before pointed out. 
It is confidently believed that when these relations or polari- 
ties, between the ascending and descending, or, as Professor 
Dana terms them, the Holozoic and Phytozoic classes, have been 
further studied, new and interesting features will be revealed. 
Thus, the resemblances between the Tunicates and Lamelli- 
branchiates are too obvious to indicate. 
Among the Brachiopods and Gasteropods, beside what has 
been pointed out, we have unlooked for similarities, as for 
instance Discina and Calyptraa, or Terebratula and Hyalea. 
Among the Polyzoa and Cephalopoda, though no polarities are 
brought to mind, except those given above, yet we cannot help 
remarking how strong the resemblance is between the Polyzoa 
and Protozoa, through Vorticella: and if Vorticella belongs to 
Polyzoa, as Professor Agassiz appears inclined to believe, a few 
steps more bring us to the Ammonitic forms of the Rhizopods. 
This is speculative (though suggestive), as it is now considered 
by many that the Protozoa forms a fifth Sub-Kingdom. 
considering transverse sections of the sacs, as shown in 
Series III, we obtain a like order of polarity. Thus the highest 
orders in Polyzoa and Cephalopoda presents a circular section. 
Brachiopoda and Gasteropoda are transversely oval; Tunicates 
and Lamellibranchiates are longitudinally oval, or in lower 
forms circular; while the Monomyarians have the dorso-ventral 
diameter in excess, and the transverse diameter reduced to the 
minimum. 
In considering the position, or angle of the antero-posterior 
axis of each class in nature, we obtain similar results (Series IV). 
Polyzoa and Cephalopoda, we place in a horizontal position, 
ing a swimming Dibranchiate for comparison: this may be 
premature however. 
Brachiopods and Gasteropods with posterior pole sme @ ele- 
S vated, as in Cyrtia and allied forms of Brachiopods, and any 
_ eoiled Gasteropod for example. Tunicates and Lameilibrancbi- 
Ps eee J 
