sinrini.iM \ Kin'Knii.viw 111 



sense (irp;ans wliose I'uiictioii is the detoction of disturhaiices iti (lie 

 water. The hiteral-hiie canals are continuous with similar canals 

 upon the head. Together these constitute the lateral-line 

 systeni of sense organs. 



Study the surface of the animal with special reference to tlie 

 following features: (1) shape of head; (2) mouth, jaws, and teeth; 

 (3) nostrils; (4) eyes and the state of lids; (5) external e\ndence of 

 ears; (0) pores of endoUimphatic ducts, one on either side of the 

 middle line of the head just caudad of the eyes, communicating 

 with the inner ears; (7) gill slits, their numbers, relations, and 

 the location of the functional respiratory tissue; (8) spiracles, 

 caudad of the eyes, and their relations; (9) the mesal or unpaired 

 fins comprising a first and second dorsal and a cniidnl or tail fin 

 the relation of which to the end of the body should be determined, 

 this relation being known as that constituting the heteroccrcal 

 toil; (10) the paired fins, those of the shoulder region called the 

 pectoral fins, those of the hip region, the pelvic fins. In male 

 dogfishes, the mesal side of each pelvic fin is modified into a stout 

 process called the clasper which is used by the males as an intro- 

 mittent organ while transferring the seminal fluid to the females. 

 All the fins possess flexible supports called the dermal fin rays, 

 embedded in the skin of the fins. 



Draw the left lateral aspect, labeling all the parts mentioned 

 above as far as they may be seen from the exterior. 



If time permits, a further study of the shark may be made 

 independently. 



Class Pisces. — The class Pisces includes aquatic vertebrates 

 which in numerous ways are readily distinguished from elasmo- 

 branchs (sharks and rays). In this connection reference might 

 be made to the presence in fishes of an operculum or gill cover 

 concealing the gills and gill slits. Within the class one may 

 recognize four subdivisions. The most numerous and widely 

 spread of the piscine types constitute the subdivision called the 

 Teleostei or bony fishes, since the skeleton is formed almost 

 entirely of bone. 



Although the directions which follow refer specifically to tiio 

 yellow perch (Perca fiavescens), they may be used in the study 

 of almost any bony fish. Most of the observations can be made 

 on preserved material, but it is desirable that observations be 

 made also upon living specimens tluring the progress of the 

 laboratorv studv. 



