322 ELEMENTARY BIOLOGY. [CHAP. 



edges enclose a ciliated groove which leads directly 

 to the oral aperture. 

 / Scrape off a little of the epithelium of the intestine; 

 mount in eosin and examine under a high power. 

 Note the presence of cilia. 



Should difficulty be experienced in following the 

 coils of the intestine, recourse may be had to injec- 

 tion. Mix equal parts, by bulk, of plaster of Paris 

 and water, stir well and strain through fine muslin ; 

 inject with a small syringe per anum. 



D. The gills or branchiae. 



a. Cut out one of the gills and examine it under 

 water; it will be found to consist of two lamellae 

 united by their ventral edges and enclosing a 

 central cavity, which opens into the epibranchial 

 chamber above. The gill-cavity is subdivided by 

 partitions, which pass from one lamella to the 

 other, and carry the larger blood-vessels of the 

 respiratory plexus. 



b. Carefully isolate a small piece of one lamina ; 

 mount in water and examine with i inch obj. 

 It will be seen to be traversed by a great number 

 of small perforations, whose walls are supported 

 laterally by short chitinous rods; the substance of 

 the gill is permeated by a meshwork of large 

 vessels. 



c. Examine under a higher power: the margins of 

 each cleft are lined by a ciliated epithelium. 



E. The excretory organ (organ of Bojanus). 



Remove the animal from its shell and pin down 

 through the adductor muscles. Dissect off the pallia! 



