112 A GUIDE FOR THE STUDY OF ANIMALS 



25. The story of the early life of Louis Agassiz ; of 

 D. S. Jordan ; of C. H. Eigenmann ; of Bashford Dean. 



26. Goldfish : their origin ; how to care for them. 



27. Fashions in fish tails, old and new. 



.:28. Development and variation in scales; fashions in 

 scales. 



29. The common orders of fishes, with examples. 



Primitive Chordates 

 Materials, 



An acorn-tongued worm, a lancelet, a lamprey, a shark^ 

 and a perch. If individual specimens are not available, 

 the pupil's text-book and charts are to be used. 



Observations. 



Acorn-tongued worm : Notice the very simple form and 

 structure of the symmetrical body, the " proboscis," the 

 collar surrounding the neck with its simple rod of cartilage, 

 the marks of internal gills and gill sUts extending some 

 distance along the body, and the presence or absence of 

 sense organs. The acorn-tongued worm {Balanoglossus') 

 lives in the sand of the seashore and in shallow water in 

 temperate and tropical regions. 



Lancelet : Observe the form of the body, of the fin, and 

 of the mouth ; note the presence or absence of sense 

 organs, and find out the number of gills or gill slits. The 

 lancelet {Amphioxus) is similar in habit to the acorn- 

 tongued worm. By day it lies buried with only the 

 mouth exposed, but at night it swims actively about. It 

 is somewhat more confined to the tropics. 



Lamprey : Observe here also the primitive or unspecial- 

 ized form of the body, of the fin, of the jawless mouth, 

 the number of gill slits, and the sense organs. 



Shark: Examine the body, noting its form and dif- 



