BY R. J. TILLYARD. 799 



distal end, thougli tlie peripliet-yof the soft cliitinous bulb, in this 

 case, projects out well beyond the outline of the star. Tlius the 

 bulla is a higher specialisation from the original macrotrichion 

 than is the dolicliaster, and can be developed from the latter by 

 further softening of the chitin forming it, and further swelling 

 up of the internal cavity. 



The dolichaster may also be compared ver}'^ closely with a 

 typical scale, such as is found upon the bodies of Collembola, or 

 upon the wings of Lepidoptera. If the dolichaster were to 

 become flattened down upon itself symmetrically from the side, 

 it would differ ver}^ little from a scale; the longitudinal edges or 

 rays would become the longitudinal stride of the scale, and the 

 sharp distal points of the dolichaster Avould remain as a series of 

 distally projecting angles, such as are very commonly found in a 

 large number of Lepidopterous scales, particularly amongst the 

 Heteroneura. 



Besides the dolichasters, the body of the larva in Psychopsis 

 carries, in a number of places where the chitin is very soft, an 

 immense number of minute, star-shaped structures, which I shall 

 call micrasters (Greek iJ.iKp6<i, small; and wrri'jp). Where they 

 occur, they are developed from every single hypoderm-cell in the 

 neighbourhood, and are thus many times more numerous than 

 the dolichasters of the same region. The micraster is a minute, 

 sessile, flattened stai-, not set upon any definite papilla, and 

 raised but little above the general surface of the integument. 

 Text-flg.7 shows a set of four micrasters with four, five, six, and 

 seven rays or points respectively. 



The micrasters vary from 1 to 3/x in height, and from 8 to 12/x 

 in extreme width. Thus they are always smaller than the basal 

 papillse of the dolichasters, which range from 12 to over 20/x in 

 width. 



It can be easily seen that the micraster is simply a specialisa- 

 tion of the minute microtrichia which occur normally upon many 

 parts of the body of an insect, especially in the sutures and 

 other places where the chitin is soft, in the form of tiny hooked 

 hairs. A search over the larval integument of Psychopsis shows 

 that, for the most part, these njicrotrichia are only feebly de- 



