28 BULLETIN OF THE BUREAU OF FISHERIES. 



Later it becomes a part of the roof. Figure 23 is a diagram representing the nature of 

 the burrow and an area with the top removed to show the general appearance of the 

 lower epidermis, which forms the floor of the burrow. 



In the case of the leaves of Castalia odorata the larva is obliged to bite the epidermis 

 to pieces and remove it by sections because of its thickness. The head is applied at 

 different angles and pieces of varying sizes are removed. Those that are small enough 

 are swallowed and the rest are used in the construction of the sides and top of the burrow. 

 The large spines are also removed and woven into the burrow with silk. On account 

 of their relatively large size they greatly tax the strength of the larva. The thickness 

 of these leaves is considerably greater than that of Brasenia leaves and the work of 

 excavating greater. This necessitates a much greater thickness in the layer of silk 

 making up the bottom of the burrow, especially as its bottom is at a higher level than 

 the lower epidermis of the leaf. The castings are utilized in the same way as explained 

 above for Brasenia, and the parenchymatous cells are eaten as food. The above changes 

 in the method of procedure show a marked contrast to the habits of many other insect 

 larvae. This ability to adapt themselves to a variety of conditions has doubtless been an 

 important factor in the adoption of their present unusual feeding habits. The pupal 

 burrow is essentially similar to the larval burrow in structure, but is made up more 

 largely of silk, is larger in diameter, and persists longer than the larval burrow (fig. 24). 



RESPIRATION. 



The larva breathes by means of four blood gills located on the posterior part of the 

 last segment. These gills are longer and more pointed than in the species having red 

 blood (fig. 15). The water in the burrow while small in amount is kept in circulation 

 by an undulating motion of the body during the intervals while the larva is not feeding. 

 The current flows from the head backward over the gills and out through the chinks 

 in the sides of the burrow, passes forward over the surface of the leaf in thin films on 

 either side, and again enters the open end of the burrow. The water should be well 

 aerated, since it is exposed in thin films both to the air and to the surface of the leaf 

 while flowing forward outside of the burrow. It is also exposed to favorable conditions 

 for the desired exchange of gases while within the burrow, as it comes in contact with 

 the air in the air-containing spaces of the parenchyma which is rich in oxygen and 

 poor in carbon dioxide. That the oxygen supply is rich seems to be demonstrated by 

 repeated accidental experiments where leaves were submerged overnight with the result 

 that the larvae died in the submerged leaves but lived in those on the surface. 



The pupa is active and continues to aerate its burrow by occasional undulations 

 of its abdomen. The repiratory filaments consist of several much-branched tufts 

 located on each side of the thorax. 



FEEDING HABITS. 



The larvae feed intermittently. They find an abundant food supply at hand, and 

 the only limit set them is the rate at which digestion can be carried on. They are yel- 

 lowish white in color, their blood lacking the haemoglobin which gives the characteristic 

 color to the other chironomid larvae which are known as bloodworms. The green food 

 material can be readily seen through the translucent body. It is seldom that the 



