268 



HARDWICKE'S SCIEN CE- GOS SIP. 



variety of compositiou of comets and meteors, aud 

 the very various degrees of nearness of approach to 

 the sun's surface by them, very different effects 

 must be expected to take place in different cases. 



We have here a fairly wide field for future obser- 

 vation and research, for it would still remain to 

 discover whether this supposed cause of increased 

 heat acts directly or indirectly. The action of the 

 sun upon comets is very great, strangely varied, and 

 easily noticed, and it may well be that some reci. 

 procal action is produced upon the sun's surface by 

 them that may be observable. I may hint here that 

 the observation of the solar spots at and near the 

 time of the perihelion passage of a comet might 

 throw some light upon this problem, as, if my 

 theory is correct, some disturbance of the solar 

 atmosphere is to be expected. Had the sun's 

 surface occupied the attention of astronomers as 

 much as the movements of comets have done, it 

 would have been comparatively easy to test the 

 suggestions now thrown out ; but unfortunately 

 bright comets appear so rarely that the establishing 

 of such a theory must necessarily occupy a con- 

 siderable interval of time. We arc forced rather 

 to depend upon collateral evidence, upon the fitness 

 of the hypothesis to fill a void previously noted, or 

 to connect together into a consistent whole facts 

 already acknowledged. In some respects this last 

 is claimed for the speculations I have made upon 

 the probable uses of comets. The nebular hypo- 

 thesis appears to receive from them some much 

 needed support on the one hand, and on the other 

 the meteoric theory of the maintenance of the 

 solar heat, to which it serves as a connecting link, 

 blending the two theories into one. The popular 

 belief in cometary heat has received a possible 

 explanation, aud the opposite constitution of comets 

 and nebulae pointed out as significant. It is of the 

 utmost importance that no fact should be distorted 

 in order to give a colour to a theory insecurely 

 based, and this I have been most careful to avoid. 

 One or two assertions have been made in opposition 

 to previously accepted opinions, which it is open to 

 the reader to accept or reject as he may see reason 

 for so doing ; but it is certain that the discussion of 

 these points, whichever way they may be decided 

 eventually, can result only in the establishment of 

 truth. 



As one of the strongest evidences of design in 

 the creation must ever be that each individual part 

 of it has its appropriate function to perform, and 

 actually serves a most useful purpose, we are bound 

 to show that both comets and meteors either are, 

 or have been, of eminent service in the develop- 

 ment or maintenance of our own system, or else 

 to yield this argument to our opponents. I have 

 suggested certain uses for these bodies, which, so 

 far from contradicting any known fact of science, 

 may fairly be taken as in agreement with the most 



advanced state of knowledge, at the same time that 

 I have contributed some ideas which '.indicate, as 

 I believe, the direction in which scientific discovery 

 must tend in future. 



Oncell Park Observatory. 



A ERESH-WATER POLYZOON. 



{LopJiopus crystallina.) 



THIS beautiful Polyzoon, of which I send a 

 sketch, was obtained from a dyke near the 

 paper-mills at Chartham, about three miles from 

 Canterbury, on July 9th, 1874. 



The Lophopus is one of the largest fresh-water 

 Polyzoa known. When exserted they are about 

 ^th of an inch in length, aud are found attached 

 to the roots of Callitriche verna, duckweeds, aud 

 other fibrous roots in shady dykes of slow-moving 

 water, under thick masses of floating plants ; for 

 in their habits they are light-shunning animals, 

 and are always on the under-side of aquatic plants. 

 They are [very beautiful microscopic objects, and 

 their being perfectly transparent renders them 

 most interesting animals for examination, as the 

 formation of their statoblast (/) can be seen in 

 their different stages of growth, from their first 

 appearance as a little swelling (at which stage 

 they are quite colourless) to their perfect form, 

 when they become detached aud fall free in the 

 perigastric space {I), having become gradually 

 coloured, the centre of a dark brown, and the 

 margin a rich yellow. The process of their pro- 

 pagation by gemmation or budding, by which 

 young ones are added to the existing colony of 

 living Polyzoa, can be plainly seen; while the 

 statoblasts (/) are designed to propagate the 

 species in the following spring, and are liberated 

 from the Polyzoon at its death, when the trans- 

 parent sac is decomposed, and the statoblast 

 escapes aud sinks to the bottom of the water. 



The perfect transparency enables us to witness 

 the internal operations of their system. The 

 action of the stomach in the process of digestion 

 can be observed with great clearness. The contents 

 are seen at times to consist of small desmids, such 

 as Closterium Lunula, Havicula^andother disc-shaped 

 and globular bodies, together with decayed ve- 

 getable matter, &c. As the action of cilia on the 

 expanded tentacles causes a current of water to set 

 in towards the mouth {a, h, h), bringing with it the 

 food required; and if in the vortex thus formed 

 there should be any large aud objectionable pieces, 

 they are prevented from entering the mouth by a 

 quick lashing motion of the tentacle, which rejects 

 and throws them out of the reach of the vortex. 

 The accepted morsel passes directly into the 

 oesophagus (^), from thence i^to the stomach (c), 

 where it is digested by the up-and-down motion of 



