BORING LIFE 



145 



cause the roof is perforated by a regular series of fine holes 

 (Fig. 32) Hke minute " man-holes " which probably help 

 the animals within to maintain the necessary circulation 

 of water within the burrow. The female appears to do 

 most of the work, for, though there are usually a pair of 

 Gribbles in each burrow, the female is invariably at the 

 head end. When the males are touched they will crawl 

 backwards slowly out of the burrow, but the females on 

 similar provocation will brace themselves firmly against 

 the side of the cavity by means of their broad tails and 

 successfully resist attempts to pull them out. Probably 



Entrance ftespirafory 



to burrow pifs 



FemcJe 



Ma/e 



Sea, 



tvCLter 



Fig. 32. — Diagram to show method of burrowing of the Gribble, Limnoria. 

 Slightly enlarged. 



they brace themselves in this manner when boring, for 

 essentially the same purpose as the Shipworm uses his 

 sucker-like foot. 



Instead of the myriads of minute eggs which the Ship- 

 worm discharges, the female Gribble only produces about 

 twenty or thirty eggs but she takes very good care of these 

 and incubates them in a special " brood-pouch " beneath 

 her body. There the developing Gribbles remain till 

 they have reached a relatively large size and when they 

 finally hatch out they are about one-fifth the size of their 

 parents and are fully formed animals capable of proceeding 

 immediately about their life's business of boring. They 



