206 



KNOWLEDGE 



[November 1, 1892. 



Fl&. 1.— Head of Buffi-Tip 

 Caterpillar (Pfigara bvcephala), 

 with jaws open : «, lobes of face ; 

 4, clypeus; c, part of labium; d, 

 labrum ; e, mandibles ; f, antennse. 



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largely^to evaporation, so that the perfect insect is, as a 

 rule, both smaller and lighter than the caterpillar which 

 produced it. After caterpillar days are over there is no 

 further growth in the sense of mere increase in bulk, but 

 only in the sense of development, i.e., gradual, though it 

 looks like sudden, change of form of already existing organs, 

 or the acquisition of new ones at the expense of matter 

 already present in the organism. 



Let us look now at the general structure of a caterpillar. 

 Whatever be the peculiarities of its actual outline, its 



more or less cylindrical and 

 ^., worm-like frame is obviously 



/ \ divisible into two very un- 



equal parts, head and body, 

 the latter being again sub- 

 divided by constrictions at 

 regular intervals into twelve 

 segments. The head (Fig. 1) 

 is covered with a hard skin, 

 the greater part of the area 

 of which is di\dded into two 

 equal lobes {a), one on each 

 side ; from their position and 

 their often highly-polished 

 appearance they are rather 

 suggestive of eyes, and are 

 sometimes supposed to be 

 such, an idea which is quite 

 erroneous ; the true eyes 

 are twelve in number, six 

 minute glassy knobs (Fig. 2) being placed on one side and 

 six on the other, not far from the mouth apparatus. A 

 lens is needed to see them properly, even in 

 a large-sized caterpillar, and from their low 

 position and their minute size they can 

 hardly be of any great use to the insect ; 

 indeed, the groping movements of its fore 

 parts, when it is not actually on its food- 

 plant, seem to indicate a purblind condition, 

 so that it probably conducts its movements 

 as much by the sense of touch as by that 

 of sight. That caterpillars are, however, 

 sensitive to light to some extent has been 

 shown in various ways. For example, the 

 caterpillars of the small tortoiseshell butter- 

 fly [Vanes-m urtica), when kept in a glass 

 cylinder before a window, have been found to 

 take up their quarters on the side nearest the light, and 

 when the cylinder was turned round so as to bring them 

 over to the other side, they quickly shifted their position 

 and assembled again in the sunlight. It is to be remem- 

 bered that this species, when on its food-plant, the common 

 stinging nettle, delights to cling round the topmost parts 

 in the full glare of the sunshine, so that in confinement it 

 was but endeavouring to follow out its own natural 

 instincts. On the other hand, such species as feed in a 

 more or less retired position would, no doubt, under 

 similar circumstances, have sought the darkest corners of 

 their prisons. Platean has conducted experiments with 

 the view of determining the extent of the visual powers of 

 caterpillars and other insects. As a result of these experi- 

 ments, he has been led to believe that the eyes of cater- 

 piOars are able to do more than merely distinguish light 

 from darkness, and that the insects really do see, though 

 but poorly. They are, in fact, very near-sighted, their 

 distance of distinct vision being no more than about a 

 centimetre, that is, imder half an inch, quite far enough, 

 however, to enable them to see to eat their food. At 

 greater distances they can perceive large masses, but do 



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Fig. 2. — 

 Cluster of 

 ocelli of Silk- 

 worm Cater- 

 pillar; right 

 side. 



not seem to be able to make out their nature. Moving 

 bodies also do not affect them except within the range of 

 distinct vision. Caterpillars seem to have a certain sense 

 of direction ; at any rate, they have a tendency to crawl 

 upward, even when the route taken does not lead to their 

 food-plant, a circumstance which appears to imply a 

 recognition of the fact and direction of gravitation. 



In the angle between the receding edges of the above- 

 mentioned lobes is situated the rh/prus (Fig. 1 , i), a triangular 

 area which forms the upper boimdary of the feeding appa- 

 ratus. On its lower edge abuts a movable lid, the lahrum 

 ((/), or upper lip, which guards the entrance to the mouth 

 above. Immediately below this is the most important part 

 of the whole apparatus, a pair of exceedingly stout jaws, 

 or mandibles («), which are placed at the sides of the mouth, 

 and when closed meet in front of its aperture. The lower 

 border of the mouth is constituted by the lahinw (c), or 

 lower Up, a complex structure formed by the coalescence 

 of many parts. There is a central portion, which is the 

 Idhium proper, with a pair of minute appendages, its palpi. 

 The two side parts are the niK.eillm, and these also carry 

 palpi. On the central portion is the minute perforation 

 which forms the opening of the ducts from the silk glands, 

 whence issues, in the form of a thread, the gummy sub- 

 stance that is used for such a variety of purposes in different 

 species, as for example, forming the cocoon or the attach- 

 ment of the chrysalis to some support, binding leaves 

 together to form a shelter, or creating a common dwelling- 

 place in the form of a thick web, or serving as a means of 

 anchorage and a ladder for return when a fall fi'om the 

 food-plant takes place. Finally, at the outermost edge of 

 the mandibles are placed a pair of small jointed organs, 

 similar to the palpi in structure, and capable of " tele- 

 scoping up " ; these are the antenna? (Fig. 1, /), which are 

 much used in testing the path and surrounding objects. 

 Close by the antenna? are situated the eyes, or rather ocelli. 

 To verify these points it is well to secure as large a cater- 

 pillar as possible, since at the best of times none of the 

 structures referred to are other than small. Insects such 

 as the larva of the goat moth {Cossu.s lifiniperda) which 

 formed the subject of Lyonet's anatomizing a century ago, 

 or the privet hawk moth (Spliin.v liijustri) which served a 

 similar purpose to Newport half a century later, answer 

 very well ; or in default of these, large specimens of that 

 extremely abundant creature, the larva of the bufl'-tip 

 (Pi/g>rra bwep/iala), which in our own times furnished Sir 

 •John Lubbock with material for a careful study of cater- 

 pillar muscles, may be used. 



{'To be continued.) 



THE REV. JOHN MICHELL, ASTRONOMER 

 AND GEOLOGIST. 



By .John Richard Sutton, B.A.Cantab. 

 {Continued from jiai/e 191.) 



AT forty-two years of age Michell settled down as 

 Eector of ThornhiU, Yorks, a small parish on the 

 River Calder, between Huddersfield and Wake- 

 field, memorable for its connection with the 

 heroic royalism of the Saviles,'' to whom the 

 gift of the living belonged. Michell seems to have 

 made the acquaintance of a member of this family at 

 Cambridge, for a certain George Savile, of Queen's 

 College (who was afterwards " Baronettus," and probably, 

 therefore, the son and heir of Sir George Savile, of Thorn- 

 hill), took the M.A. and LL.D degrees together in 1749f 



* Whitaker's Loidis and Elmete. t Cantabrigietise.'s Graduati. 



