between numbers 4 and 5. After one month, board No. 1 and the control 

 are removed and taken into the laboratory for study and new boards 

 are put in their places. At the end of the second month, board No. 2, 

 which has been submerged for 2 months and the control, which has 

 been submerged for one month, are removed for study and new ones put 

 in their places. The following month, board No. 3, submerged for 3 months 

 and the control, submerged for one 

 month, are removed and replaced by 

 new ones. This procedure is con- 

 tinued down to the last board which 

 has now been submerged for 6 or 

 more months and the control for 

 only one month. From this series of 

 boards it is possible to ascertain the 

 speed of growth of the borers over 

 the breeding seasons. 



In northern waters a collecting 

 panel having 12 boards may be suc- 

 cessfully used to give a growth pic- 

 ture over a period of a year. For 

 comparative studies several panels 

 should be submerged at the same 

 time in any given region and the 

 collecting should be continued over 

 a period of several years as condi- 

 tions and the extent of the attack 

 seem to vary markedly from year to 



year. In tropical waters, however, a 



board one inch thick would probably 



be destroyed in less than 6 months. 



Consequently, in order to get a con- 

 tinuous picture throughout the year, 



it may be necessary to submerge 



panels having only 6 boards or less 



and run 4 or more panels concur- 

 rently. Thus the first panel would 



be submerged in January and run to 



June, the second would run from 



March to September, the third from 



May to November and the fourth 



from July to January. The duration 



of submergence and the exact depth 



at which the panels are hung must 



be determined by the individual 



doing the collecting as local condi- 

 tions are so exceedingly variable. 



IE 



"1 



ULLJUU 



3-- 



csht 



Pig I — Monthly collecting board de- 

 signed by Dr. W. F. Clapp, Clapp 

 Laboratories, Duxbury, Mass. 



Fig. 2. — Laminated collecting board. 

 Face view. 



Fig. 3. — Laminated collecting board. 

 Side view. 



(52) 



