106 



KNOWLEDGE 



[May 2, 1898. 



limited distribution. Tiie mangrove swamps of the tropics 

 are distinguished by a highly remarkable crustacean fauna. 

 The weed of the Sargasso Sea may be regarded as a kind 

 of floating shore. It has its own crabs and shrimps. 

 Turtles and hairy crabs play the part of floating islands 

 to a considerable population, and an anchored buoy is 

 often rich in amphipods among its fringing weeds. 



To the general policy of concealment above described 

 there are some ex- 

 ceptions. On the 

 open shore the sessile 

 cirripedes called 

 Balani make no pre- 

 r^ '•iT''^^^^^m tence of hiding. Being 



cemented to the rock, 

 they cannot run away 

 if they would, and 

 they have little reason 

 to wish for the power. 

 The hermit crab may 

 say, like an EngUsh- 

 uian, " My house is 

 my castle" ; but the 

 Balanus is a castle in 

 itself. Six rigid in- 

 terlocking valves 

 make a stout wall 

 round about it, and 

 the movable valves 

 above, through which 

 from time to time 



Flaf/iarthriis lloffmannseygii (Braudt). ^'^^ delicate cirri pro- 

 From ants' nest, South of England, trude, can be firmly 



closed down at the 

 top. Great stretches of coast-margining rocks are coated 

 with colonies of these Balani. But there are many 

 other situations in which cirripedes occur. Like the 

 spider, which impartially fastens its web to the rafter of a 

 cottage or the ceiling of an imperial palace, the cirripede 

 plants itself on the body of a whale or the carapace of a 

 crab, on the iron sides of a merchantman or on a piece of 

 pumice. It will cluster in dense masses round an old 

 floating bottle, and some of the small species crowd the 

 mouth-organs of crab or crawfish, with easy security, 

 wuere tbny might seem to be running into the jaws of 

 death. The sau3age-like PuchtjhdAla carcini is parasitic on 

 the tail part of Can-inus mcEnm, the above-mentioned 

 shore crab, and within reach of the claws of its ho.-t. 

 Now, if there is one thing more than another about which 

 toe sLoie crab is touchy, it is about having its tail part 

 drawn away from its breast, except by the intervening 

 ma-»s of its own numerous eggs. No doubt the heartless 

 Pachtjbdella, brainless impostor though it be, is all the while 

 making believe to be the eggs of the deluded shore crab. 

 But the afflicting behaviour of parasites is too extensive a 

 subject for the end of a chapter. 



Of inland Crustacea there is much to be told, of which 

 only a hint or two can here be given. Several of the groups 

 are but poorly represented in our own islands. Apart 

 from Entomostraca, our fresh waters can boast of a crayfish 

 and here and there a prawn, of the isopod Asclluti communiii, 

 and of a few Amphipoda in rivulets, lakes, and wells. We 

 have nineteen species of terrestrial Isopoda, these wood- 

 lice including the small Platyarthrus Ho/mannsrijijii, found 

 only in ants' nests — blind, slow moving, white ; and the 

 delicate Trkhonim-ius roscjte— nimble, rose-coloured, and 

 rare. Exotic species of sessile-eyed crustaceans may 

 chance to be found in our botanic gardens as they have 

 been in France. But no land crabs are likely to disturb 



our picnics, requiring as in Panama the flourish of a 

 cudgel to repress their effrontery. No river crabs ascend 

 the summit of Helvellyn to match those found at similar 

 heights in Himalayan ricefields. No little mole of a cray- 

 fish burrows under our flower beds, as in Tasmania. We 

 have no prawns like those of America, which rival the size 

 of large lobsters ; or like those of the Ganges, concerning 

 which the Asiatic complacently observed to the fastidious 

 Englishman, " Prawn eat nigger — nigger eat prawn." No 

 hermit crabs on our hills confront the geologist as they. do 

 in the West Indies, marching about among the bush in 

 large and heavy shells transported from the beach a 

 thousand feet below. No Binnis latro, strange hermit 

 without a shell, is here seen competing for cocoanuts as in 

 the islands of the Pacific. But notwithstanding some 

 deficiencies, our position is extraordinarily favourable for 

 the study of Crustacea. The extensive seaboard with its 

 many sheltered bays and inlets and harbours ; the variety 

 of climate from north to south and from summer to 

 winter ; the diftering depths of water roimd our coasts ; the 

 ebb and flow of tides ; the mud, the sand, the weeds, the 

 rocks, the stones of the shores ; the frequent occurrence of 

 wooden piles for piers or breakwaters, of buoys and other 

 floating objects ; the abimdance of fish and of empty shells, 

 severally enable us to accommodate a multitude of 

 crustacean species out of proportion to the space our 

 islands cover on a map of the world. To become familiar 

 with the names and with the nature, with the habitat and 

 with the habits, of all these species, will be found a task 

 the more inexhaustible the more absorbing the industry 

 brought to bear upon it. 



NEBULA AND REGION ROUND y CASSIOPEIyE. 



By Isaac Roberts, d.sc, f.r.s. 



THE photograph covers the region between R.A. 

 Oh. lom. and R.A. Oh. 55m. 57s. ; declination 

 between 59° :2r and 6F 2' north. Scale — one 

 millimetre to twenty-four seconds of arc. 



Co-ordinates of the fiducial stars marked with 

 dots for the epoch a.d. 1900. 



star (.) D.M. No. Hi Zone -t-eo" E.A. Oh. 47m. "-Ss. Dec. N.eO"" 3S-9 Mag. 5-0 

 „ (..) ., H« „ 59» „ Oh. .50in. 4.V0s. „ 19° 49-3' „ 6-3 



,.(•.) „ 157 „ 6iy „ Oh.olm 161s. ., 60»531' „ 70 



,.(::) ., 161 ,, 50' ,, Ou. 53m. Sr-jj. „ 5a» 5S 3 „ 7'i . 



The photograph was taken with the twenty-inch reflector 

 on 1895, October 25th, between sidereal time Oh. 16m. and 

 Ih. 46in., with an exposure of the plate during ninety 

 minutes. 



On the north following side of / are two nebulae having 

 the outlines of cones or fans, with faint nebulosity between 

 them, which on the negative can be traced nearly the 

 whole distance between one nebula and the other ; the 

 apexes of the nebulae are bright, and the brightness 

 diminishes gradually into invisibility as it expands outwards 

 from the conical ends. The nebula farthest from the 

 north is brighter than the other, and both have a cloud- 

 like struct'ire, with many stars of between the ninth and 

 seventeenth magnitudes involved, apparently, in them. 



The following are the measured position angles and 

 distances of the nebulfe. 



Position angle from 7 of the faint star touching the 

 apex of the conical end of the northernmost nebula, 

 14° 20' 12 ' ; distance from 7 22' 16". Position angle of 

 the faint star touching the apex of the other nebula, 

 57° 84' 51" ; distance from 7 19' 19". 



A photograph of the region here referred to was taken 

 on 1890, January 17th, upon which the two nebuhe were 

 faintly, but distinctly, shown ; and I have compared the 



