132 



HARDWICKE'S SCIENCE-GOSSIP. 



NOTES ON THE DEVELOPMENT OF THE 

 GNAT {TIPULA PL CMOS A), LINN. 



By Harry Thomas. 



I FIRST found the larvoe on the carcases of some 

 dor-beetles I had fished out from a water-butt 

 in my garden. 



Shortly afterwards, my brother found a cluster of 

 the eggs attached just beneath the surface of the 

 water, to the side of a neighbouring water vessel. 

 We did not then know that these eggs were in any 

 way related to the larvae, until a close examination of 

 the living larvre that hatched out from them, revealed 

 their close similarity. Later we secured specimens of 

 the eggs and larvae from a tank in a garden at Bettws 

 y Coed. 



The female lays her eggs, arranged spirally in a 



and two transparent threads, twisted with each other, 

 may be traced from the neighbourhood of the lower 

 to the upper extremity, where they unite and are 

 continued beyond, as a single thread terminating in 

 an adhesive disk (Fig. 51). The eggs appear some- 

 what oval in form and are arranged in a spiral which 

 shirks a complete turn and when all but round makes 

 a loop and goes back again. The nearly completed 

 rings thus formed lie each within a separate segment- 

 Trie following notes on the development were taken 

 from superficial observations of the specimens beneath 

 the microscope, without any previous preparation. 



Fig- 5'. 



sausage-shaped, colourless jelly, varying from \ inch 

 to I inch in length beneath the surface of still waters. 

 I obtained specimens during the months of August, 

 September, and the early part of October. They 

 were found usually attached to the side of the vessel, 

 by an adhesive disk terminating a prolongation at 

 their upper extremity, just beneath the water : but 

 sometimes unattached, suspended several inches 

 beneath the water, when the disk reaches to, and 

 floats upon the surface. When first deposited, the 

 eggs are closely packed together, forming a short 

 brown string. In a very short time the connecting 

 envelope absorbs the surrounding water till it has 

 increased to many times its original bulk. The eggs 

 then become separated and form an inner spiral chain. 

 Slightly magnified, the egg-case appears divided into 

 many equal segments by narrow transparent rings, 



Development Within the Egg. 



The egg presents in profile a convex upper and a 

 flattened lower surface (these terms, upper and lower,, 

 are applied simply for convenience). Looking down 



: ' " . 



Fig. 52. 



■'" •»-'& V.*. *5 v - : • %;*.,. 



.> ,'.A ■ '"*■' 



I \% 



' ' <. 



Fig- 53- 



Fig- 54- 



upon it the appearance is oval. The shell is somewhat 

 elastic, and is perfectly transparent and structureless, 

 so that the development of the embryo may be easily 



observed. 



First Day. October \<,th. 5 P.M. — Examined a 

 few minutes after the eggs were deposited ; each 

 contains yellow granular yolk for the most part, but 

 at either extremity, colourless protoplasm. The cori- 

 tents fill completely the enclosed space (Fig. 52). 



7.30 P.M. — The contents have receded slightly from 

 both extremities of the shell, farther from one than 

 the other. The colourless protoplasm is observable 

 at one extremity only, the opposite appears bilobed. 



9.30 P.M. — The yolk granules have retreated from 

 these two lobes, and other similar though smaller 



