RESUME OF THE STAGES OF DEVELOPMENT 89 



Spawn of the first week of July is in the straight-hinge stage of the larva 

 in the second week, entering the umbo stage in the third week, and ap- 

 proaching full size in the fourth week. The abundant spawn of the second 

 week of July accounts for the numerous grown larvae of the second week of 

 August. The decline in spawning towards the end of July is responsible 

 for the diminution in numbers of larvae at the end of August. 



Spatting (fixation of the larvae to solid objects) begins about a month 

 after spawning, keeping parallel with and exhibiting fluctuations similar 

 to both spawning and swarming. The first minute spats found about the 

 middle of August are likely to be already several days old and to have come 

 from eggs spawned in the second week of July that became developed into 

 full-grown larvae in the second week of August. This will allow the really 

 first spat, to go unobserved on account of being few and scattered and leave 

 the last two weeks of August for the completion of development and spat- 

 ting of the late larvae, which in a backward season may lag into September. 

 Judging from a comparison of 1904 and 1909, when the reproductive pro- 

 cesses are kept back by cold weather for a time they move all the more 

 rapidly when fine weather does arrive. In 1904, on July 11, larvae meas- 

 ured 12 to 20 (-083 mm. to -138 mm.) and the first spat was observed on 

 August 16. In 1909, on July 22, larvae measured 10 to 14 (-069 mm. to 

 •096 mm.) and the first spat was observed on August 19. 



