STATIC TISSUES 



211 



sen.r. 



bos. 



the highest development being reached, probably, in the statocysts of 

 the active cephalopods where the two organs are much enlarged and the 

 epithelium is much differentiated. It is possible that part of it has an 

 auditory function in the squid. This animal has its two " otocysts " 

 (we shall hereafter term them " statocysts ") enlarged into spaces of 

 some size and considerable differentiation as to shape. Several bars 

 of the surrounding capsule of cartilage project into this space ; and the 

 epithelium which lines it, while it is 

 thin and undifferentiated in most 

 regions, has several strongly special- 

 ized portions. The use of these 

 highly differentiated portions can be 

 partly inferred from the habits of 

 the animal. No creature has better 

 control of its swift movements and 

 rapid changes of position, whether 

 swimming in schools at sea or in 

 following the twisting and turning 

 of its agile prey, the mackerel, and 

 other fish. It is probable, therefore, 

 that the best-developed sensory epi- 

 thelium of this statocyst is used to 

 record and so control its motion. It 

 is improbable, although possible, 

 that the statocyst has some auditory 

 function to perform. 



The most specialized of the lining 

 epithelium is found on the median 

 posterior side of the sac. Here the 

 cells have formed several layers, the 

 most distal of which lie in several rows and are provided with nu- 

 merous rods which resemble cilia in appearance. As all other classes 

 of mollusks have moving cilia in this position, it is possible that these 

 rods move and are cilia, or at least are modified cilia. The intra-cellular 

 portions of these rods are furnished, inside the cell, with several rows 

 of spindle-shaped enlargements or knobs known as blephroplasts (Fig. 

 191). The sensory cells lie among more numerous sustentacular cells. 



A layer of cells containing ganglion cells lies beneath these perceptory 

 cells and separates them from the underlying capsule of cartilage. 



The insects undoubtedly have great static powers. Their life and 

 actions show this. And yet no great specialization of any tissue for this 

 purpose has been found. The only case in which such an organ has 

 been surmised is in the Diptera or flies. These animals have the rudi- 



FIG. 191. Static sensory cell from the stat- 

 ocyst of a squid, Loligo Pealii. nu., nu- 

 cleus; sen.r., sensory rods; bas.gr., basal 

 granules of two grades. (From a draw- 

 ing by A. F. McCLiNTOCK and E. W. 

 BIXBY.) 



