PROCEEDINGS OF THE NATIONAL MUSEUM. 



In certain parts of the body there are found invaginations of the 

 chitinous, external .skek>ton serving as advantageous points for the 

 attachment of muscles. These can best be seen on the meso and 

 metasternal plates of winged species of Thripid^e, and are darker than 

 the plates in color. Many species show a narrow, transverse line 

 across the second to seventh dorsal al)dominal plates near the anterior 

 edge of each. This dark line is caused by a chitinous, ridge-like 

 thickening forming an arch on the inside of each of these plates. 



The chitin of the skeleton is rarely entirely unpigmented. Pig- 

 mentation may take })lace in the cuticle itself, when the color is usually 

 gra}', yellow, brown, or black, or color may appeal* from pigments 

 deposited in the hypodermis or fat-body. Such deposits are, usually 

 very irregular and of a yellow, red, or purple color. Pigments are 

 frequently present in both places in the same individual. Metallic 

 colors do not occur. 



Larra. — The chitin of the larva is much less firm than that of the 

 adult, and there is scarcely an}^ difl'erentiation in texture or structure 

 between the plates and connecting membranes. The surface is not 

 reticulated, but is usually considerably wrinkled transversely and 

 roughened, though sometimes it is quite smooth. 



Pigments are rarely present in the chitin of the larva, and when 

 they do occur the colors seem to be limited to gray, yellow, or brown. 

 Larvfe are usually of yellow or red color, but these colors are due to 

 h3'podermal or fat-body pigments, and to some extent, perhaps, to the 

 body fluids. 



Pupa. — The delicacy of the chitinous covering of the early stages 

 can be seen during the period of transformation. It is then thin, 

 smooth, and often shining. The cuticle forms a delicate sheath around 

 the wings, antenna?, and legs, and toward the end of this stage can be 

 plainly seen separated from the body of the inclosed adult. 



hiteg amental f/j}j)end(((7e.'^.— These are present in the form of hairs, 

 bristles, or spines which are variously modified. They are frequently 

 borne upon small warts or tubercles which can be most distinctly seen 

 upon the cheeks of many Tubulifera. The membranes of the wings 

 are thickly set with microscopic hairs, usually either darker than the 

 membrane itself or sharing its color. In some species {Sencothri^fy. 

 various species) the abdomen is also thickly set with microscopic hairs, 

 giving it a sleek, velvety appearance, and whorls of similar minute 

 hairs often mark the antennal segments. The posterior fringes of the 

 wings are always composed of long slender hairs, usually more or less 

 spiral or wavy in appearance and inserted either directl}" into the edge 

 of the wing (Tubulifera) or attached by a joint to a fixed base upon the 

 edge (Terebrantia). This joint allows of motion only in the plane of 

 the wing and toward its tip; it facilitates the folding of the hairs into 

 line with thfe edge of the wing when the latter is brought to rest. 



