56 LABORATORY DIRECTIONS IN 



abdomen is also a group of fused segments. Make out these reigons in 

 Metargiope and Miranda, or other spiders. 



In the centipedes and millipedes, on the other hand, all of the seg- 

 ments are movable except a small number in the head. Examine a 

 specimen of Scolopendra or Julus,and note that the region behind the head 

 is flexible. 



10. Phylum CHORD ATA (Lat. chordatus = having a chord or cord). 

 The most commonly known animals because they are large and con- 

 spicuous and some of them are domesticated. 



Characteristics. 



10a. Backbone composed of vertebrae (or a notochord) present. 

 Examine skeleton of a bird, a cat, a frog, a fish, and a snake or lizard. 



106. Typically two pairs of jointed appendages. Recall the modi- 

 fications of these appendages found in the skeletons studied in Homology. 

 Observe also the modifications of the limbs in the skeleton of a mole; of 

 a seal; of a porpoise; and (if available) of a snake. 



lOc. Besides the above parts there is a general internal skeleton com- 

 posed of cartilage or bone. 



B. SUBDIVISION OF THE PHYLA 



Phyla are divided into subgroups called classes. Classes are dis- 

 tinguished from one another in the same way as are phyla, but by means 

 of characters less fundamental and less primitive than those used in 

 separating phyla. Note that this is true in the analysis of one subphylum, 

 the Vertebrata, in the following exercise. 



The Classes of Vertebrates 



1. Class PISCES (Lat. piscis = fish). 



Characteristics. 



la. Cold blooded, aquatic, respiring by gills. Observe the gills in 

 a fish. 



16. Body long and pointed, and provided with dorsal fins, tail fin, 

 ventral fin, and two pairs of lateral fins. Verify in a specimen. 



Ic. Scales cover the body; and a flap, the operculum, covers^the gills. 

 Verify. 



2. Class AMPHIBIA (Gr. amphi = both + bios = life). Frogs, toads, 

 salamanders, newts, etc. 



Characteristics. 



2a. Cold blooded animals usually spending part of their existence in 

 water, part on land, capable of living either in water or on land. 



