Scientific Lectures. 221 



their respective groups were also tlie lowest. Agassiz lias beanti- 

 fully illustrated this among the edimoderins and fishes ; the earliest 

 fishes had tails, in which the vertebral column terminated in the 

 npper lobe of the caudal fin, like the sharks ; while fishes of higher 

 structure have the vertebral column terminating at the root of the 

 caudal fin. Yet, if you will examine a young trout, just hatched, 

 you will see that the tail resendjles that of the shark in this 

 feature. 



In order to illustrate another principle of classification, I will first 

 make you acquainted with some of the various modes of locomotion 

 in the animal kingdom, and first and lowest of all is the locomotive 

 egg. Among many of the lower animals, the e^g is supplied M'ith 

 cilia, by which it is carried through the water and assists in its wider 

 dissemination. Among the lower plants the same feature is recog- 

 nized, and the spores of "many sea weed are propelled through the 

 water by means of this primitive, though effective apparatus. ( These 

 cilia are like little membraneous hairs that thickly clothe the exterior 

 of the l^ody, and by their rapid vibration urge it through the water. 

 They are microscopic.) AVe may rightly conclude that ciliary 

 motion is the lowest mode of propulsion of an animals, and so find 

 that among the protozoa t])is mode is conspicuous. I need only to 

 delineate a few of the infusoria so common in stagnant water to indi- 

 cate this feature. Xow, while these low forms depend u])on the 

 presence of cilia to propel them, a little higher in the scale the same 

 peculiar ciliary membrane assists only in exciting currents of water to 

 flow to the mouth, whereby particles of food are brought within its 

 reach, or within its stomach and intestnio ; the nutritive matter is 

 circulated by the same means. 



Another form of locomotion is seen in the amreba, one of the 

 sim])lest of animals. The body has no stomach, no locomotive organs, 

 in fact we might say has no organization, resembling more a drop of 

 thin glue tlian anything else, and yet this little animal can move, and 

 can ingest and digest food. It moves by certain portions of its body 

 expanding or projecting, and then the remaining portions contracting 

 to it. And while it is dragging itself along it may at any time engulf 

 in its folds particles of food, which are rapidly digested, and any por- 

 tion of its body may at any time improvise a temporary stomach. In 

 other members of this simple group the animal fabricates a beautiful 

 shell of microscopic proportions, though of such remarkable structure 

 and sintnilar resemblance to the nautilus and ammonite that fur along 



