Very many have also the stinging property of the nettle; but, whether the cause of this is chemical or mechanical, is not yet exactly known.
SECOND CIRCLE. VASCULAR, SEXUAL ANIMALS.
3186. So far, or in the ascending scale up to the Acalephæ, the animal is only viscus with an absorbent canal, which is at the same time a canal of evacuation, without a distinct intestine being set apart for that purpose; such is the general rule.
3187. After the Acalephæ the formation undergoes a change; the distinction between the exterior and interior is prominently displayed, and the internal wall becomes freed as a separate and perfect intestine along with a mouth and anus; the external wall appears as a free tegument. But, seeing that two concentric and separated cysts could not subsist without combination by means of the nutritive system or the vessels; a perfect vascular system is formed, divided into veins, arteries, and hearts.
The tegument, wherein the vessels become self-substantial, is the branchial membrane. There is therefore placed around the intestinal body a vascular body also, or branchial membrane, which is consequently pleura or mantle (pallium), as in the Mussels. The body of the intestine consists of intestine and peritoneum; that of the vessels of branchiæ and pleura or mantle.
These animals are hence bisystemic, being both Intestinal and Vascular animals; but, since the vascular system is a new addition, it is thus characteristic of the circle, and its members must be therefore called Vascular animals. With the vascular system, however, all its further developments have been bestowed; thus especially the complication of the vessels with the intestinal ramifications or, in other words, the liver—Hepatic animals. The salivary glands also are a similar complication, and in this series therefore they make their appearance.
Lastly, the renal glands are such a kind of vascular organ, or branchiæ of the sexual parts; they also begin to be astir in this series.
With the separation of the systems into separate teguments or membranes, the sexual parts also separate. The ovarium becomes an independent organ furnished with its own excretory ducts; the male parts are individualized to form veritable testes furnished with excretory ducts, or even with a penis. Still this is all effected only by degrees, or as yet within the confines of this circle.
These animals divide according to the viscera into Venous, Arterial, and Cardiac animals; according to the sexual parts, into Ovarial, Orchitic, and Renal animals.
Class 4. Venous, Ovarial Animals.