166 CHORDATA. 



note the beating of the heart (the heart is on the right side) and 

 the frequent reversal of the direction of the pulsations. The 

 endostyle, longitudinal ^pharyngeal folds, intestine, gonads, gono- 

 ducts, renal organ, and suhneural gland are also visible through 

 the mantle. 



6. Note the muscle hands of the mantle which serve to con- 

 tract the body and especially the siphons. Where are the mus- 

 cles best developed? Is there any definite arrangement of the 

 muscle-bands ? 



7. Fix a large specimen by pins through the siphons, and 

 with scissors and fine forceps remove a large section of the man- 

 tle from the left side, injuring the underl3ing jpharynx as little 

 as possible. The large space between the pharynx and the 

 mantle, laterally and dorsally, is the atrium, or peribranchial 

 chainher, which is formed as an ectodermal involution. Into 

 this atrial cavity open the intestine and the gonoducts, and also 

 the numerous stigmata of the pharynx. 



Alimentary Canal. — Cut out a piece of the wall of the pharynx 

 from a very fresh specimen and examine in sea-water with a 

 microscope. 



1. Note the meshwork of blood-vessels, and the openings or 

 stigmata, lined with actively moving cilia. Of what use are these 

 cilia? 



2. On each side of the pharynx six longitudinal pharyngeoJ 

 folds will be seen. 



3. The endostyle is a ciliated groove along the mid-ventral 

 wall. Anteriorly it is continuous with the peri-pharyngeal cili- 

 ated bands, which encircle the oral end of the pharynx. From 

 the point where they unite dorsally the dorsal lamina extends 

 backward along the mid-dorsal line of the pharynx. At its 

 posterior end will be seen the small opening into the esophagus. 



Do you understand how the animal captures its food and 

 how the endostyle, peri-pharyngeal bands, and dorsal lamina are 

 used? 



4. In front of the anterior end of the dorsal lamina note the 

 small, volute-shaped dorsal tubercle. This is the extremity of 



