42 



absence of settled iuforruation about the limbs and internal structure of 

 tribolites considerable difficulty has been experienced in their classifica- 

 tion. Barrande based his classification of the various genera on the 

 characteristics of the pleurae. But Salter considered this distinction 

 artificial ; for though the exterior of the ribs be smooth, there are often 

 indications of grooving on the under surface. Salter based his 

 classification on — (1) The nature of the facial sutui-e ; (2) the structure of 

 the eyes ; (3) the number of segments in the body. The lecture was 

 concluded by a description of many of the principal genera, and was 

 illustrated by large diagrams, numerous specimens, and the splendid plates 

 from Bari'ande's " Le Systeme Silurien." 



Meeting held in the Library of the Philosophical Hall, March 3rd, 

 1890. Professor De Burgh Birch, M.D., CM., F.E.S.E. (President), in the 

 chair. • 



THE DEVELOPMENT OF THE FLY OF CHIRONOMUS. 

 PROFESSOR L. C. MIALL, F.G.S., F.L.S. 



In the introduction the lecturer briefly described the life-history of the 

 Larvae of Chironomus. It belongs to the Diptei-ous order of insects. 

 When full grown it is about one inch in length, and is of a reddish colour, 

 and is popularly but erroneously called the blood worm. It is found in 

 ditches and other collections of water, and feeds on vegetable matter. It 

 is not provided with any means of defence, but has a strong p)-opensity to 

 burrow in the mud at the bottom, which is doubtless a most eflectual 

 protection against other carnivorous forms. This habit of burrowing has 

 in all probability been the result of diminishing the growth of the 

 Tracheal system, common to most aquatic larvae of insects, but which in 

 chironomus is very rudimentary, and confined entirely to the first 

 segment, after the head, or what is known as the prothorax. At the 

 hinder end of the body are three tubercles, which have a significant 

 relation to this mode of life. With the aid of a remarkably complete 

 series of lantern slides, the first and subsequent indication of the 

 transformations from the larva to the pupa, and afterwards the Imago 

 (one of the perfectly harmless gnats), was clearly and interestingly 

 shown. The development of the compound eyes or facets which takes 

 place in the larval period, and their immediate connection with the 

 antennary bulbs, was admirably studied. The impoi-tant organs of 

 chironomus were also shown in sections, giving a greater idea of the 

 development of the bead, legs, wings, and respiratory appendages in the 

 life-history of this insect. A short account was given of the reproductive 

 organs which are present in the larval stage, and can even be traced back 

 to the earlier development of the egg. 



