2 THE POPULAR SCIENCE MONTHLY. 



the stomach, intestine, heart, and other organs of vegetative life. This 

 is shown in Fig. 3. 



Let us now go one step further and learn what kind of a verte- 

 brate is the gar-pike. At present the most natural primary subdivi- 

 sion of the branch seems to be into three great groups. The liighest 



Fig. 2. Part of the Side op the Body of Lepidosteus platystomus, 



Natural size, showing the arrangement of the enameled scales. Below is an outline of a single 



scale ; the point is covered by the scale in front. 



is the Mammalia, comprising our common quadrupeds, also bats, mon- 

 keys and men, seals and whales. The females of all these bring forth 

 their young alive, and nourish them with milk. 



Next come the Sauropsida, including birds, turtles, crocodiles, 

 lizards, and snakes. Lastly, the Ichthyopsida, embracing the Ba- 

 trachians (frogs, toads, and salamanders), and all other vertebrates. 



Evidently, our gar-pike is neither a mammal nor a bird, a turtle, 

 a snake, nor a lizard. It does look a little like an alligator, but it has 

 not only fins and scales, but also gills ^ which are not known to exist 

 in any reptile ; while all the Ichthyopsida have gills during at least a 

 part of their lives. The gar-pike is neither a frog nor a toad; it has 

 scales and fin-rays unlike salamanders. Why, then, not call it a.Jish f 



Fig. 3. Cross-Section (Natural Size) of the Short-nosed GAE-riKE {Lepidosteus plafys- 



tomvs), 



Showlntr the general arrangement of the organs which is characteristic of vertebrates. The sec- 

 tion is made in front of the ventral flns at the point indicated by Xon Fig. 1. The cut sur- 

 face is looked at from beliind. Near the middle is the vertebral column or backbone (VC). 

 Above it i? the spinal cord (6'0, surrounded by bony walls. Below are the abdominal viscera. 

 A is the median aorta. T' V the lateral veins. J/A is the median channel of the air-bladder, 

 and LA, LA, are its lateral chambers. The cavity of the stomach (Al) is on the left, and the 

 liver (L). with two veins, on the ri^'ht. O, O are the two ovaries, of which tlie left lies far- 

 ther forward so that its section is smaller. The whole is surrounded by the muscular walls 

 of the body (M,M, M, M), and this again is covered by the plates of the skin. 



