3394 



MOSS ANIMALS AND LAMP SHELLS 



the marine Chilostomata or lip-mouthed Bryozoa, of which the sea mat (Flustra 

 foliacea), common in the North Sea, is an example. The magnified cells shown in 

 the illustration represent the harder portion of the animals, into which the soft 

 anterior portions can be withdrawn. The openings through which the tentacles 

 protrude lie crosswise, and each is provided with a lip-like elastic lid. Each indi- 

 vidual can thus take refuge within its chamber and close the lid. Other genera 

 which, unlike Flustra, have no lid, can close the aperture by means of muscles. 

 The colonies of sea mats form branched leaf -like lobes very common at the seaside, 

 and often mistaken for seaweed. Each side of the leaf consists of a layer of closely 

 crowded individuals. The cells only partly calcify, so that when fresh they are 



elastic, and the whole stock remains very 

 flexible. To this suborder belong also 

 Retepora and Lepralia, before mentioned. 



An important rise in the scale of or- 

 ganization is found in the Gymnolsemata, 

 especially in the lip-mouthed forms, where 

 a marked division of labor takes place; that 

 is to say, the individuals which constitute 

 the stock vary in structure and fulfill differ- 

 ent physiological functions. There are 

 structures known as zocecia, stolons, avicn- 

 laria, vibracula, andovzcells, some perhaps 

 all of which are modified individuals. 

 The zocecia are the normal individuals of 



a. Stock (natural size); *- Five cells (magnified), the Colony, fully developed for mOSt of the 



functions of life; respiration, taking in 



food, and digestion, and no doubt also for receiving sensory impressions. The 

 stolons have a much humbler function, but are indispensable for the well-being of the 

 colony. They are rootlike outgrowths of the stock, consisting of very simple indi- 

 viduals which serve for attaching the whole colony to foreign objects, such as stones, 

 shells, etc. The most remarkable are the structures known as avicularia, so called 

 because they resemble the head of a bird. The individual is turned into a pair of 

 forceps, of which the large upper blade (very like the skull and upper jaw of a 

 bird) and the smaller lower blade (like the lower jaw) constantly open and shut by 

 means of a complicated arrangement of muscles. These avicularia are movably 

 attached by a short neck, and are found near the entrance to a zocecium. They turn 

 from side to side, snapping in all directions, and, no doubt, every now and then 

 catch some of the small worms, crabs, or larvse which rest on the colony. The vic- 

 tims are held till they decay, and, as they break down, fragments are drawn into 

 the mouth by the water currents caused by the cilia on the tentacles. These dead 

 creatures act as baits, and attract other victims within the influence of the same 

 stream. These also are drawn into the mouth. On account of these peculiar 

 structures, the Chilostomata have been called the bird's-head corallines. Equally 

 interesting again are the vibracula, long thread-like structures, attached by short 

 stalks, which keep up a constant whip-like motion. Their function is not clear; but 



SEA MAT (Flustra foliacea). 



