14 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



C. BALANOGLOSSUS 



i. External anatomy. — Obtain a specimen, place in a dish of water, and 

 examine. (As different species differ somewhat in appearance, the following 

 description applies only to Balanoglossus [Dolichoglossus] kowalevskii.) It is an 

 elongated wormlike animal about five or six inches in length. The body is 

 divided into three parts — the proboscis, the collar, and the trunk. The proboscis 

 is the slender, conical, pointed structure at the anterior end, used by the animal 

 in burrowing into the sand. The collar is the band encircling the body just 

 posterior to the proboscis. The mouth is concealed within the collar. The 

 trunk comprises the greater part of the animal and presents a more or less 

 ruffled appearance. The median ventral line is marked by a distinct longitudi- 

 nal band; the median dorsal line in a similar but less distinct manner. The 

 sides of the trunk for about an inch and a half posterior to the collar project 

 somewhat and are slightly different in appearance from the rest of the trunk; 

 these projections contain the reproductive organs and hence are named the 

 genital ridges. Between the anterior portions of the genital ridges on the dorsal 

 side will be found two longitudinal rows of small parallel slits, the gill pores. 

 (The true gill slits, leading from the pharynx, are U-shaped and each opens into 

 a chamber, the gill pouch, which in turn communicates with the exterior by means 

 of the gill pore, which is somewhat smaller than the gill slit. In some balano- 

 glossids, as Ptychodera, the U-shaped gill slits open directly to the exterior, as 

 is the case in the larva of Amphioxus. The structure and development of the 

 branchial region of balanoglossids is strikingly similar to that of Amphioxus.) 

 The remainder of the trunk is occupied by the digestive tract and possesses a 

 terminal anus. The species under consideration lacks the hepatic caeca, a 

 series of outgrowths of the intestinal wall, figured in P and H. Make a drawing 

 of the animal from the dorsal side. 



For further details consult P and H, pages 2-7; CNH, Vol. VII, pages 3-21; 

 H, pages 512-14; N, pages 60-65. 



D. ANATOMY OF A LAMPREY 



The lampreys belong to the lowest class of true vertebrates, the class Cyclo- 

 stomata, or round-mouthed fishes. 



1. External anatomy of a lamprey.— Place the specimen in a dissecting 

 tray. The body consists of a stout cylindrical head and trunk and a flattened 

 tail. From the median dorsal line in the posterior portion of the body arise 

 two dorsal fins, while the tail is provided with a caudal fin, continuous with 

 the second dorsal fin. The fins are supported by numerous fin rays, slender 

 parallel cartilages usually visible through the skin. There are no paired 

 ventral fins such as are found in the true fishes. The skin is soft, slimy and 

 jiaked. 



