AND THEIR TRANSFORMATIONS. 83 
dark ground. This last-mentioned peculiarity has led to the insects of this genus being named by collectors 
*hair-streak butterflies.” 
No genus has ever more strongly proved the great advantages to be derived from a minute, analytical examination 
of the different organs of insects than the present. For want of such an examination in the structure of the feet, 
which in this group affords sexual differences, the males of the beautiful species represented in our 24th Plate are 
described in all previous works on English butterflies as the females, and vice-versa. Even by Messrs. Curtis and 
Stephens, who introduce the structure of the fore feet into the characters of the genus, they are described as 
‘alike in both sexes.” For our knowledge of the peculiarities existing in these organs in the different sexes we are 
indebted to Dr. Horsfield, who was accordingly enabled to determine the sexes of the species with precision. The 
male anterior tarsus consists of a single long joint ; which is as long as the entire articulated tarsus of the female, 
and when covered with scales might easily be regarded as similarly articulated. The intermediate thigh is also 
furnished with a remarkable tooth near the extremity, and there is a corresponding notch in the tibia. 
In preceding pages (9 and 23), I have described the two different plans adopted by elongated Caterpillars in 
order to effect their transformation beneath a girth across the middle of the body. The caterpillars of the present 
family, by their short wood-louse form, at first sight present far more apparent obstacles to the accomplishment 
of such a proceeding. We have only to fancy to ourselves a very stout little man with his arms bound to his 
sides, and his legs tied together, laid upon his belly on the ground, and whilst in that situation compelled to attach 
a rope on each side of his body, carrying it across his back and then undressing himself. Reaumur has, however, 
so carefully and circumstantially described the proceedings of a species of this genus*, that we are enabled to bring 
the whole process before our mind’s eye. When the period for the transformation of the insect is arrived, the 
caterpillar attaches itself by the tail, and shortening the fore part of the body by contracting the segments 
considerably, it emits an arched thread from the extended spinneret of its mouth, which it attaches at one side of 
the head: it then carries the thread to the other side, having the instinct to extend it to a fit length in order that 
when the process is complete the body may neither be too much tightened nor too loose for support. After 
attaching a number of threads by passing the head backwards and forwards, emitting a continuous thread from 
the mouth during the process, a skein of between 50 and 60 threads (as Reaumur supposes) is formed, of a fit 
length, attached at each end at the sides of the head ; which, as already stated, is drawn considerably backwards, 
owing to the great contraction of the anterior segments of the body. In this consists the chief difference between 
the proceedings of these insects and those of the swallow-tailed and cabbage butterflies, described in our previous 
pages, the head of the caterpillars of those species, owing to the slender form of the body, being thrown over the 
back, or greatly elevated. During the process of spinning this skein of thread, the caterpillar has contrived to 
insinuate its head beneath them, so that the skein rests upon the scaly back of the head, and when the skein is 
completed it gradually pushes the front of its body beneath the skein, pressing its body down as closely as possible, 
until it contrives that the middle of the body shall be girt by the skein. The difficulty is apparently increased by 
the very great delicacy of the threads, and by the body of the larva being clothed with strong short bristles. When 
completed, the skin of the caterpillar bursts, and the pupa appears, the process of getting rid of the old skin being 
similar to that adopted by the other girt caterpillars of the butterflies mentioned above. 
* Linneus gives Reaumur’s insect as his Papilio Pruni, but thisit can scarcely be, for Reaumur’s description does not accord with that species, 
and Reaumur found his larve on the elm. 
