206 



The Philippine Journal of Science 



1913 



its siphon for breathing purposes, while that of the Tabanus 

 was functional. The Tabanus, obtaining a secure perch by 

 dragging itself and the prey above the water, devoured the 

 mosquito wriggler in a few minutes. In another instance the 

 weight of the culicid pulled its captor under the water to 

 the sandy bottom a distance of nearly 30 centimeters. Here 

 the Tabanus showed its superior vitality by remaining attached 

 for nearly two minutes until apparently assured of the immo- 

 bility of its prey, then, releasing its hold, the Tabanus larva 

 struggled to the surface where it rested with siphon extended. 

 The mosquito larva meanwhile moved feebly several times, and 

 succumbed within a few minutes. 



This adaptability is lost, however, in the developed larva which 

 becomes more slothful in movement and grub-like in superficial 

 appearance. Both extremities, the head and the siphon, become 

 obtuse in form, and the ventral protuberances functioning as 

 prolegs become more truncated. Growth after the second molt 

 becomes noticeably less in length and more in thickness. The 

 greatest growth observable was shown to be between the periods 

 of the first and the second molts. 



The following table is given to show the normal growth of a 

 larva. The measurements and the critical stages of life are 

 indicated : 



Table I. — Progress of development of a larva. 



Date. 



Length. 



Stage of develop- 

 ment. 



Sept. 15 



■mm. 



1.6 



1.8 



3.0 



4.0 



5.0 



6.5 



11.0 



20.0 



22.0 



25.0 



27.5 



29.5 



27.5 



17.5 



At birth. 

 1 day old. 



After first molt. 



Second molt. 

 Mature larva. 

 Pupa, third molt. 



16 



20 



21 



22 - 



23 



26 ...:- 



30 



Oct. 8 . 



9 



12 



17 



21 - 



24-_ 





In all biological accounts of the Tabanidse there appears to 

 be one phenomenon which is uniformly noted. This is the 

 remarkable difference in growth shown by individual flies of 

 the same species. The only process in the development which 



