104 



KNOWLEDGE. 



[June 1, 189S. 



tenrecs among the insectivores ; and in the echidnas 

 among the egg-layers. From the perishable nature of 

 these appendages we have, luifortunately, no evidence as 

 to the existence of spines among fossil mammals ; but, 

 from the foregoing considerations, we are strongly inclined 

 to think they may be mainly characteristic of later 

 epochs. 



In this connection it is interesting to notice that the 

 spiny globe-fishes {Diodon, &c.), often termed " sea-hedge- 

 hogs," in which the spines are bony and therefore capable 

 of preservation, do not date back below the tertiary, and 

 that spiny fishes are unknown in earlier epochs. More- 

 over, some — although by no means all — of the palfeozoic 

 sea-urchins appear to have had very minute spines. Hence, 

 it would rather seem as though the history of spines has 

 been exactly the opposite of that of bony armour, which, 

 as we have shown in our article on " Mail-Clad Animals," 

 hag tended gradually to disappear with the advance of 

 time. 



Finally, we have to notice the general similarity in 

 appearance of so many of the more specialized spiny 

 mammals, due not only to their bristling coat, but likewise 

 to the general shortness or absence of the tail, and the 

 rounded, plump form of the whole body. The bearing of 

 this independent development of spines in so many groups 

 of mammals, together with the acquirement of a general 

 external resemblance in the creatures thus clothed, on 

 questions of wider import, will (with the editor's permis- 

 sion) form the subject of another article, in which we 

 shall also have to take into consideration the conclusions 

 reached in our previous communication. Before doing this, 

 we may, however, have to lead further up to the subject 

 of " parallelism " by a third article. 



CATERPILLARS' DWELLINGS.-IIL 



By E. A. Butler. 

 {Continued from page 87.) 



THE third division of our subject deals with soli- 

 tary caterpillars which construct portable cases, 

 intended to be their constant, and, in some 

 instances, life-long abode. As the caterpillar 

 walks about, the whole of its body, except the 

 front segments, to which its legs are attached, is enveloped 

 in the case, which is therefore trailed along behind it. 

 While feeding, a similar arrangement is made, but at other 

 times the whole insect is concealed within. Case-making 

 caterpillars are not, as a rule, large insects, and in this 

 country they are almost without exception small species, 

 some of them very minute. The habit is practised chiefly 

 by species belonging to the section Tine», the same that 

 contains the little ermine moths already described. Outside 

 of this group there is, amongst British insects, only one 

 other family in which the habit appears, and tlu-ij are a 

 most extraordinary set of creatures. They form the family 

 I'sychidtr, which is represented in Britain by only a few 

 small insects ; in tropical regions the species are more 

 numerous, and many of them much larger. 



On the trunks and twigs of trees may sometimes be seen 

 what look like Lilliputian bundles of sticks, each bundle 

 being only about half an inch long, while the stick-like 

 fragments of which it is composed are many of them much 

 shorter than this. On puUing at one of these little piles 

 we find that the fragments are all fastened together into 

 one mass, and that the bundle adheres sUghtly to its 

 support, but it comes away on the application of a little 



Fio. 9.— Case of 

 Fsi/rh id, adhering to 

 fragment of leaf ; 

 magnified two dia- 

 meters. 



force. These bundles are the cases of the Psi/rhidce. (Fig. 9). 

 Examination shows them to consist of small stick-like 

 fragments of vegetable substance, such as stems of grass 

 and stalks of leaves, which have been collected by the 

 caterpillar, and fastened to the outside of a silken tube. 

 Within, the tube is beautifully smooth, its walls being 

 tapestried with silk. From the opening at the larger end 

 the caterpillar protrudes the front part of its body, enough 

 only to enable it to hold the food and 

 eat. On opening such a case, it would 

 be found to have different contents, ac- 

 cording to the time of year. In May 

 the inhabitant would be a caterpillar ; 

 later on, a chrysalis ; and still later, 

 at about the end of June or in July, 

 nothing more than fragments of an 

 empty chrysalis shell would be found 

 if the insect whose home it was had 

 been a male, but if a female, there 

 would be found a caterpillar-like crea- 

 ture as well. The explanation of this 

 is, that while the male of these in- 

 sects is a four-winged being like other 

 moths, the female has no wings at 

 all, and looks very much like a 

 caterpillar herself, or sometimes, owing to the absence of 

 legs as well as wings, more like a maggot or short fat 

 worm. The females of this group are in fact the most 

 degraded of all Lepidopterous insects ; the males of our 

 British species are rather obscure-looking creatures, of a 

 brownish or blackish colour, whence some of them are 

 known as " chimney-sweeps." 



Being utterly helpless and unable to fly, the female 

 never trusts herself outside the walls of her cell, but 

 remaining immured in darkness for the whole of her adult 

 life, receives in that position the attentions of her mate, if 

 she should be lucky enough to meet with one. But such 

 good fortune is by no means the lot of all. The males are 

 far less common than the females ; in fact they seem to be 

 almost a superfluous luxury amongst the Psychidie, for the 

 opposite sex find no difBculty in continuing the race 

 without the assistance of partners. In other words, the 

 curious phenomenon of parthenogenesis, or the production 

 of fertile eggs by virgin females, prevails to a surprising 

 extent in this group of moths, so that it is possible to 

 breed them generation after generation and year after year 

 without ever seeing a male. The larva of the male Psyche, 

 on the approach of pupation, fastens his case to a leaf or 

 stem by silken threads round its mouth, thus guarding 

 against any mischance during the period of his own help- 

 lessness. He then turns round within his case and faces 

 its free end before casting his last larval skin, so that he 

 may be ready, when he becomes a moth, to make his exit 

 at the only available opening, that at the free end, which 

 had previously served for the ejectment of waste matters. 

 Like a Tortrix, therefore, he leaves his chrysalis case pro- 

 jecting partly from his dwelling when he abandons it for 

 ever. 



A continental species makes a spirally-coiled case, the 

 silken walls of which are strengthened with particles of 

 sand and other adventitious matter. In shape it somewhat 

 resembles a small snail shell. Certain exotic sjDecies from 

 Africa make cases which still more closely imitate the 

 shells of the MoUusca, some being like a flat snail, and 

 others like the pyramidal shells of some of our pond snails 

 (Fig. 10). The larger exotic species are often called 

 " basket- worms," in allusion to the basket-like house in 

 which they are always found, and which, when they are 

 resting, hangs down from the twigs and branches of trees. 



