392 MR. R. OWEN’S REMARKS ON THE ENTOZOA. 
lation in the disc of Rhizostoma, &c. ; a structure which, when compared to the di- 
stinctly developed vessels manifested in the Echinodermata, presents a strong argument 
for retaining the Acalephe in the more simple division of Cuvier’s Radiata. 
If it be true, as has been stated, that the Meduse produce not ova, but locomotive 
ciliated gemmules, we have an additional reason for placing the Acalephe among the 
Acrita, in which division of the animal kingdom only is the plant-like generation by 
gemmation external or internal, or by spontaneous fission, observed. This character 
is not, however, generally applicable to the Acrita ; for the Sterelmintha propagate by 
ova, and have appropriate organs, distinct from those of the digestive system. These 
organs are either cryptandrous, or productive only, as in Cystica and Cestoidea ; or a 
fecundating gland is superadded to the ovary, as in Trematoda; or the sexes are sepa- 
rate, as in the Acanthocephala; so as already to typify almost all the modes of gene- 
ration by which the higher classes of animals are perpetuated. 
We thus perceive in the Acrite subkingdom that, with the exception of the genera- 
tive and digestive organs, all the other systems are more or less blended together, and 
the corporeal parenchyma seems to possess many functions in common. Where a distinct 
organ is eliminated, it is often repeated almost indefinitely in the same individual. In 
the Polypi we frequently find the nutritious canals supplied with a thousand mouths ; 
and the Polygastrica derive their name from an analogous multiplication of the digestive 
organ itself. Among the Stere/mintha the generative system becomes the subject of 
this repetition, each joint of the Tenie being the seat of a separate ovary, though all 
are nourished by continuations of the same simple tubes. Again, the calcareous and 
siliceous Sponges, which, in eliminating the first sketch of an internal skeleton, seem 
to lose the few characteristics of animal life which they before possessed, are limited to 
the repetition of the same spiculum. 
The formative energies being thus expended on a few simple operations, and not con- 
centrated on the perfect development of any single system, it is not surprising that we 
should find in the Acrita the greatest diversity of external figure ; all the leading types 
of animal organization seem to have their origin in this division ; and it has been well 
observed, that ‘‘ Nature, so far from forgetting order, has, at the commencement of her 
work in these imperfect animals, given us, as it were, a sketch of the different forms 
which she intended afterwards to adopt for the whole animal kingdom!.”” Thus in the 
soft mucous sluggish Sterelmintha, we have the outline of the Mollusca? ; in the fleshy 
living mass which surrounds the earthy and hollow axis of the Polypi natantes, she has 
sketched a vertebrated animal ; and in the crustaceous covering of the living mass, and> 
the structure more or less articulated of the Polypi vaginati, we trace the form of the 
Annulosa. 
' Hore Entomologicz, vol. i. part ii, p. 223, 
2 These, however, are more immediately continuous with the composite Polypes by means of the genera Bo- 
tryllus, Eschara, and Cellaria; while the Trematoda evidently lead to the Haustellate Annelida, as the Leech, &c. 
