WERNER MARCHAND 139 



Besides, the egg masses are never found of a strictly geometrical 

 form, and numerous irregularities in details of their structure are 

 always observed. In general, however, it can be said, that the eggs 

 are placed horizontally and in rows which when observed horizontally 

 or vertically always present a more or less regular arrangement. 



On the larval stage of this species we possess the results of Lecail- 

 lon's first studies (1905), amphfied by later additions. At the time 

 of Lecaillon's studies knowledge about tabanid larvae was still very 

 meager; he believes that the larvae are predacious, and there are 

 certain species which are aquatic and others in which the larva lives 

 in the ground or in moist soil. 



Lecaillon made an attempt to raise the larvae of Tahanus guat- 

 uornotatus from the egg, but did not succeed completely, as many of 

 the larvae died in spite of all precautions; but he was able to keep 

 them alive for several months and some of them were still living when 

 the paper was pubhshed (December 15, 1905), having survived for 

 more than six months. Lecaillon made some observations on the 

 hatching of the larvae. 



According to Mann, the duration of embryonic development in this 

 species is ten to twelve days. Lecaillon placed eggs laid May 24 in a 

 moderately damp atmosphere (the stem with the eggs was simply 

 placed in a crystallizing dish), and observed that on June 6, thirteen 

 days after oviposition, no hatching had taken place. Taking two 

 eggs out of the mass, he saw, as a result of the slight pressure or 

 traction to which they had been submitted, the hatching of com- 

 pletely developed larvae. 



On the following day the egg mass was vigorously rubbed, and 

 as a result all the larvae hatched at once, showing that embryonic 

 development had been completed in all the eggs. The difference in 

 time appearing in Lecaillon's observation as compared with that of 

 Mann is said to have no significance as the duration of embryonic 

 development is very variable, in a given species, according to the 

 temperature in which the eggs are kept. 



The medium duration of embryonic development was, according to 

 Lecaillon's first publication, from twelve to thirteen days. But 

 later he found that the larvae generally do not hatch as soon as they 

 are completely developed; they may remain inside the egg shells for 



