GLOSSARY. 215 



Incurrent canal. A canal that admits water to a sponge. 



Integument. Skin; outer covering. 



Inter-ambulacral area. One of the areas of an echinoderm that lies be- 

 tween adjacent ambulacral areas. 



Inter-filamentar junction. A connection between adjacent filaments 

 in a lamellibranch gill. 



Inter-lamellar junction. A connection between adjacent lamellae in a 

 lamellibranch gill. 



Inter-radial canals. The canals of a medusa that lie midway between 

 the per-radial canals. 



Intestine. One of the divisions of the alimentary canal. 



Introvert. A portion that will turn inward, as the anterior end of 

 Phascolosoma. 



Ischipod. The third segment of a typical crustacean leg. 



Kidney. Frequently applied to the excretory organ of an invertebrate. 



Labrum. The appendages that form the lower lip of insects and some 

 other arthropods. 



Lamella. One of the two sides that form a lamellibranch gill; a flat 

 structure. 



Lamelliform. Like a lamella; thin and flat. 



Lamina. A thin plate or a scale. 



Lancet. A sharp structure; a portion of the sting of a bee. 



Larva. An embryo; a stage in the development of an animal. 



Lateral. At or toward the side. 



Ligament. The portion that unites the valves of a clam shell; an elastic 

 connection. 



Lithite. One of the concretions in a tentaculocyst of a medusa. 



Liver. Frequently applied to the largest digestive gland of an inverte- 

 brate. 



Lophophore. The disk that surrounds the mouth and bears the tentacles 

 in the Molluscoida. 



Lorica. The transparent covering of a rotifer. 



Macronucleus. The larger of the two nuclei of certain Protozoa. 

 Madreporic plate. The perforated plate through which the water-vascular 



system of an echinoderm is put in communication with the sea- water. 

 Mandible. One of a pair of mouth appendages of an arthropod. 

 Mandibulate. Possessing mandibles. 

 Mantle. The outer fold of tissue of many animals; in many mollusks and 



tunicates it secretes a protective covering. 



