62 



JIARDWICKE'S SCIENCE-GOSSIP. 



room during an English winter is more than they can 

 endure. They are strictly nocturnal, and shun the 

 light, although when long unmolested they become 

 bolder. 



The cockroach belongs to a miscellaneous group 

 of animals, which may be described as in various 

 degrees parasitic upon men. These are all in a 

 vague sense domestic species, but have not, like the 

 ox, sheep, goat, or pig, been forcibly reduced to 

 servitude ; they have rather attached themselves to 

 man in various degrees of intimacy. The dog has 

 slowly won his place as our companion ; the cat is 

 tolerated and even caressed, but her attachment is to 

 the dwelling and not to us ; the jackal and rat are 

 scavengers and thieves ; the weasel, jackdaw, and 

 magpie, are wild species, which show a slight 

 preference for the neighbourhood of man. AH of 

 these, except the cat, which holds a very peculiar 

 place, possess in a considerable degree qualities 

 which bring success in the great competitive exami- 

 nation. They are not eminently specialised, their 

 diet is mixed, their range as natural species is wide. 

 Apart from man, they would have become numerous 

 and strong, but those qualities which fit them so 

 well to shift for themselves, have had full play in the 

 dwellings of a wealthy and careless host. Of these 

 domestic parasites at least two are insects, the house- 

 fly and the cockroach ; and the cockroach in particular 

 is eminent in its peculiar sphere of activity. The 

 successful competition of cockroaches with other 

 insects under natural conditions is sufficiently proved 

 by the fact that about nine hundred species have 

 already been described,* while their rapid multipli- 

 cation and almost world-wide dissemination in the 

 dwellings of man is an equally striking proof of their 

 versatility and readiness to adapt themselves to arti- 

 ficial circumstances. In numerical frequency they 

 probably exceed all domestic animals of larger size, 

 while in geographical range the^five species, Lap- 

 ponica, Ger?nanica, oricntalis, Americana, and 

 Australasia, are together comparable to the dog or 

 pig, which have been multiplied and transported by 

 man for his own purposes, and which cover the 

 habitable globe. 



The cockroach is historically one of the most 

 ancient, and structurally one of the most primitive, 

 of our surviving insects. Its immense antiquity is 

 shown by the fact that so many cockroaches have 

 been found in the coal measures, where nearly sixty 

 species have been met with.f The absence of well- 

 defined stages of growth, such as the soft-bodied 

 larva or inactive pupa, the little-specialised wings 

 and jaws, the simple structure of the thorax, the 

 jointed appendages carried on the end of the abdomen, 

 and the unconcentrated nervous system, are marks of 



* British Museum Catalogue of Blattarise (1868) and supple- 

 ment (1869). 



t Scudder on Palaiozoic Cockroaches, Mem. Boston Soc. 

 Nat. Hist. vol. iii. 



the most primitive insect- types. The order (Orthop- 

 Ura) which includes the cockroaches, is undeniably 

 the least specialised among winged insects at least, 

 and within this order, which comprises the termites 

 or white ants, the leaf and stick insects, the crickets, 

 locusts and grasshoppers, the earwigs, the ephemeroe, 

 and the dragon-flies, none are more simple in struc- 

 ture, or reach farther back in the geological record 

 than the cockroaches. The wingless Thysanura are 

 even more generalised, but their geological history is 

 illegible. 



The eggs of the cockroach are laid sixteen together 

 in a large horny capsule. This capsule is oval, 

 with roundish ends, and has a longitudinal serrated 

 ridge, which is uppermost while in position within 

 the body of the female. The capsule is formed by 

 the secretion of a " coUeterial " gland, poured out 

 upon the inner surface of a chamber (vulva) into 

 which the oviducts lead. The secretion is at first 

 fluid and white, |,but hardens and turns brown on 

 exposure to the air. In this way a sort of mould of 

 the vulva is formed, which is hollow, and opens 

 forwards towards the outlet of the common oviduct. 

 Eggs are now passed one by one into the capsule, 

 and as it becomes full, its length is gradually in- 

 creased by fresh additions, while the first-formed 

 portion begins to protrude from the body of the 

 female. "When sixteen eggs have descended, the 

 capsule is closed in front, and after an interval of 

 time for hardening, is dropped in a warm and 

 sheltered crevice. In Periplaneta cnentalis it measures 

 about "45 in. by "25 in. TheCva develope within the 

 capsule, and when ready to escape are of elongate- 

 oval shape, resembling mummies in their wrappings. 

 Eight embryos in one row face eight others on the 

 opposite side, being alternated for close packing. 

 Their ventral surfaces, which are afterwards turned 

 towards the ground, are opposed, and their rounded 

 dorsal surfaces are turned towards the wall of the 

 capsule ; their heads are all directed towards the 

 serrated edge. The ripe embryos are said by West- 

 wood to discharge a fluid (saliva?) which softens the 

 cement along the dorsal edge, and enables them to 

 escape from their prison. In Blatta Gcrmanica the 

 female is believed to help in the i^rocess of extrica- 

 tion.* The larvffi are at first white, with black eyes, 

 but soon darken ; they run about with great activity, 

 feeding upon any starchy food which they can find ; 

 they love warmth even more than their parents, and 

 often huddle together in snug and protected corners. 



Cornelius, in his very interesting " Beitrage zur 

 nahern Kenntniss von Periplaneta orioitalis" (1853), 

 gives the following account of the moults of the 

 cockroach. The first change of skin occurs imme- 

 diately after escape from the egg-capsule, the second 

 four weeks later, the third at the end of the first year, 

 and each succeeding moult after a year's interval. 



* "Modern Classification of Insects," vol. i. pp. 421-1. 



