6 4 



ECONOMIC ZOOLOGY 



4 feet and a diameter of i inch, Fig. 45. Sigerfoos (52) estimates 

 that a single large female may lay 100,000,000 eggs. These eggs 

 rapidly develop into free-swimming larvae, typical of the lamelli- 

 branchs. After further development these larvae attach themselves 



FIG. 45. A ship-worm, Teredo navalis, in a piece of timber. Xi. p, pallets; 

 55, siphons; T, tube; V, valves of shell. (From Hegner, College Zoology, after 

 Cambridge Natural History from Mobius.) 



to some submerged piece of wood and begin to burrow into it, gradually 

 changing to the worm-like form as they clo so. The newly attached 

 larvae are tiny animals, abotft 0.2.$ mm., long; on entering the wood 

 they grow rapidly so that in about five weeks, in some species, they 



FIG. 46. Devil-fish, Octopus sp. 



may be 100 mm. long. Sigerfoos estimated that a four-foot specimen 

 was only about a year old. The rate of growth seems to be independent 

 of the kind of wood, whether it be soft white pine or hard oak; probably 

 the food supply is the determining factor. In a four-foot worm the 



