1891.] MICROSCOPICAL JOURNAL. 231 



Introduction to Elementary Biology. 



By henry L. OSBORN, 



HAMLINK, MINN. 



Part V. — A Specific Life History Considered Biologically. — 



The Frog. 



( Conthnied from fage 2og.^ 



The principles already stated are true of all living things, whether 

 large or small, high and complex, or low and simple, and beings are thus 

 all bound together into one vast realm of bodies exhibiting similar phe- 

 nomena and acting under common laws. It seems paradoxical perhaps 

 to say it, but it is none the less true that there is no power of the gera- 

 nium which is not equally possessed by the elephant, and vice versa. 

 The elephant cannot, it is true, cause delicate and odorous flowers to 

 blossom on his person, the exercise of protoplasmic powers in his case 

 are not along that line ; but he can exert the same fundamental powers 

 of protoplasm as are involved in the act on the part of the geranium. 

 It will be well for us now to consider some common organisms with a 

 view to testing whether it is made up of tissues which in turn are com- 

 posed of cells, which again in turn are protoplasmic bodies with some 

 or all of the fundamental powers of motion, sensation, metabolism, and 

 reproduction. For the first case we may take the common frog. This 

 animal is well known to everybody, has been the subject of very nu- 

 merous essays and sketches, and has perhaps been more studied than 

 any other animal in the animal kingdom. 



General Sketch of the Frog. — The frog's body presents a head 

 and trunk and four limbs, all covered with skin. The head is provided 

 with a large mouth opening into a series of organs placed one behind 

 the other, and forming a closed tube which lies within the space which 

 occupies the body. This tube, which we call the alimentary tube, has 

 various organs connected with it, and runs to the hind end of the trunk 

 where it opens by the vent. Food which is swallowed at the mouth 

 travels along the tube, is variously transformed, parts of it absorbed, and 

 the remainder passed away through the vent. The trunk cavity, be- 

 sides containing the alimentary tube, contains various other organs — 

 the heart, situated at the level of the front limbs, is connected with a 

 system of tubes which collect absorbed food from the alimentary tube 

 and carry it thence to all parts of the body, as, for instance, to the 

 brain, muscles, and to the various organs connected with the alimentary 

 system. The food used in the body gives rise to waste products which 

 must be removed to make room for fresh useable ones, and the lungs are 

 present in close connection with the blood circulation to remove car- 

 bonic adid gas from the blood and put fresh, pure oxygen in its place, 

 and remove another waste product called urea. The heart forces the 

 fluid through all the system of tubes, and thus prepared food is taken 

 from the alimentary tube to all the organs and their waste products 

 carried away from them. Besides these systems closely related to the 

 feeding of the frog's body, we have three other systems which are re- 

 lated to its commonly observed performances and are for more unusual 

 employment — the supporting system or skeleton and skin, the muscular 

 system and the nervous system, and the reproductive system. 



The supporting system is a frame-work of inflexible levers and solid 



