1896.] MICROSCOPICAL JOURXaL 411 



1. External Anatomy. — Eximine the smelt,* notic- 

 ing its plon<iate and taj'eiing shape; liow does this 

 oflfer advantasre in swimming-? There is no distinct neck 

 joinin>i: the head to the body. The following body- 

 regions can he recognized, viz: — the^eac?: with eves, mouth 

 etc; the trunk directly behind the head, it is marked by 

 containing the thin-walled body-cavity, in which tlie var- 

 ious alimentary organs lie, and limited posteriorly by the 

 cloac'i or common opening for the viscera of the body, 

 located in the middle line of the ventral surface; the _po.si- 

 abdomen, the remainder of the body behind the trunk. 

 The body is covered generally with thin and delicate 

 scales, located in definite lines; they are attached in front 

 and free behind, and placed so as to overlap; a fuller 

 study of them will come later. Examine the fins: as to 

 position they can be distinguished as mediari, and paired. 

 The dorsal fin is located in the middle of the back; the 

 caudal is the name of tiie tail-fin (the term "tail" properly 

 applies to the entire post-abdomen); the anal fin is located 

 in the ventral surface commencing at the cloaca; in addi- 

 tion to these functional fins there is a fleshy structure in 

 . the dorsal line between the dorsal and caudal fins, it is 

 the adipose fin, a rudiment of another dorsal fin. Besides 

 these median fins, there are two paired fins: the pectoral- 

 Jins are closely related to the head at the very front end 

 on the trunk region; the pelvic fins lie in the ventral sur- 

 face just below the dorsal fin. Examine the fins care- 

 fully and distinguish in them all a thin and delicate 

 fleshy portion, supported by jdeces of bone, the y?/j, rays. 

 The fin rays start togetlier in tlie base of the fin hut 

 distallv they spread out like the ])arts of a fan; the small 

 bones that compose them can be seen with the naked eye, 

 but better with a hand lens. The number of rays in a 



*In case a smell cannot be had a irout or white fish is nearly of kin 

 and can best be used. 



