282 



ried out to sea. The eggs of this species are therefore invested by a 

 gelatinous envelope, which swells out, the moment it touches the water, 

 into an abundant transparent mucilage, and the whole mass is moored 

 to some fixed object by twisted cords. The mucilage has its special 

 uses : it makes the egg-mass slippery, so that birds or insects cannot 

 grasp it ; moreover, it spaces the eggs, so that each is well exposed to 

 the sunlight and air ; lastly it keeps off the attacks of the water moulds 

 (Chytridca: and allied Oomycctes) , which abound in water and on the 

 surface of decaying plants, or devour the substance of living insects 

 and fishes. It may be that the mucilage of the egg-mass has some an- 

 tiseptic property, for it remains unchanged by parasitic growth or pu- 

 trefaction long after the eggs have hatched out." 



The general statement above quoted applies very well to Cliirouom- 

 idcc in America, though it is evident that the writers had only in 

 mind the British members of the family when they suggested the pos- 

 sibility of the eggs being swept out to sea. It is probable that their 

 theories as to the uses of the gelatinous envelope of the ^gg mass are 

 mostly correct, though I doubt its suggested efficiency in preventing 

 destruction of the eggs by birds and insects. 



The amount of time devoted to the study of the ngg stage in Chi- 

 ronomidcc has not been sufficient to permit association of the charac- 

 ters possessed by them with those possessed by the larvae, pupae, and 

 imagines. 



The number of eggs contained in the Qgg mass of seven different 

 females computed by Miall and Hammond {loc. cit., p. 154) was as 

 follows: 668, 784, 817, 828, 912, and 1102. The duration of the Qgg 

 stage, given by the same authors, is six days (p. 175). The length of 

 the tgg stage will in all probability fluctuate in accordance with weather 

 conditions. 



The method of reproduction in certain species in the genus Tany- 

 tarstis presents an instance of larval paedogenesis in this family. The 

 American species in which this occurs is given by Prof. O. A. Johnnn- 

 sen* as T. dissimilis. A European form of this genus having larval 

 paedogenetic phases has been recorded by Professor Zavrel. A species 

 of Chironormis in Europe has been recorded as having pupal paxlo- 

 genesis. 



Larval CJiaractcrs 



Head. — The dorsal surface of the head consists of three longitu- 

 dinal plates, to the median one of which (clypeus) is attached the la- 

 hrum. The labrum in the genus Chironomus has on its under surface 

 a complicated arrangement of hooks and two articulated lateral arms, 



•Science, Vol. 32, 1910, p. 768. 



