GLOSSARY 259 



Interfilamentar junction. A connection between adjacent filaments 



in a pelecypod gill. 

 Interlamellar junction. A connection between adjacent lamellae in a 



pelecypod gill. 

 Internode. In hydroids, that portion of a stem or branch between two 



branches. 

 Inter-radial canals. In a medusa, the canals which run from the 



stomach to the circular canal and which lie midway between the 



per-radial canals. 

 Introvert. A portion which may be drawn in, as the anterior end of 



Phascolosoma. 

 Ischiopod. The first segment of a crustacean endopod. 



Kidney. Frequently but improperly applied to the excretory organ of 

 an invertebrate. 



Labrum. The fused pair of appendages which forms the lower lip of 

 insects and some other arthropods. 



Lamella. One of the two sides which form a pelecypod 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. In pelecypods, the elastic structure which unites the valves. 



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



Liver. Frequently but improperly applied to the largest digestive 

 gland of many invertebrates. 



Lophophore. The disk which surrounds the mouth and bears the ten- 

 tacles in the Molluscoida. 



Lorica. The transparent covering of a rotifer. 



Macronucleus. In general, the larger of the two nuclei of ciliate Pro- 

 tozoa. 



Madreporic plate. The perforated plate through which the water- 

 vascular system of an echinoderm communicates with the outside. 



Mandible. One of a pair of mouth appendages in arthropods. 



Mandibulate. Possessing mandibles. 



Mantle. The outer fold of the body of many molluscs; the entire body 

 wall in tunicates. In both groups it secretes a protective covering. 



Manubrium. The hollow outgrowth supporting the mouth of a medusa. 



