In the form of the body, as well as in the circular position of the cephalic arms, the Sepiæ strikingly resemble their antetypes, the Acalephæ and Cirripedia, and their metatypes, the Asteriadæ and Crustacea.
With these animals the second stage or circle through which the Dermatozoa pass, or that of the Sexual animals, is closed. They require only a slight additional grade of perfection, and they would pass over into another class of animals. Thus were the arms to become horny and articulate, they would be Crustacea; had the head a nose, and the body consequently a myelon or spinal chord, they would then be Fishes.
SECOND CIRCLE. RESPIRATORY, CUTANEOUS ANIMALS—ANCYLIOZOA.
Here range the Worms, Crustacea, and the proper or volant Insects.
3502. In this circle a remarkable relation is revealed. If, namely, its classes, orders, and families be compared with those of the two preceding circles, it is then distinctly shown that the present one again commences quite from below, ascends parallel with both these, and transcends them in its highest inmates or members.
As an example of the first case, the imperfect condition of some Entozoa, and their great resemblance to Infusoria, is sufficiently expressive.
The Worms evidently pass parallel to the Mucus-animals, and the Entozoa indeed to the Infusoria, the Red-blooded Worms to the Polyps, but the Holothuriæ chiefly to the Acalephæ, near which they are still arranged up to the present day, although they are articulated, and have an intestine and vessels.
Thus this class traverses the three inferior classes, and consequently imparts to them only the value of orders, or must itself be raised only to the rank of an order, a step, however, which, considering the great number of Worms, would not be suitable or just. The names may therefore remain for the sake of uniformity; only it must be borne in mind that they are of unequal value.
The same relation is exhibited in the Crustacea or Crabs. They obviously admit of being parallelized with no other animals than the Malaco-or Conchozoa. The Entomostraca and Crabs evidently repeat the Mussels, the Aselli the Snails; but the Spiders and Scorpions the Kracken or Cephalopoda. Consequently here also the orders correspond to the preceding classes.