HARDWICKE' S SCIENCE-GOSSIP. 



193 



GRAPHIC MICROSCOPY, 



By E. T. D. 



No. IX.— POLYPIDOM OF LePRALIA NITIDA. 



HE holiday month, 

 September, affords 

 the microscopist 

 the long antici- 

 pated pleasure of 

 reaching the sea 

 — to luxuriate in 

 all its associations, 

 the terraces and 

 plateaux of rocks, 

 dredging, and its 

 mysterious lottery 

 of attractions, and 

 the enchanting 

 solitude. For fine 

 broken ground, 

 certainly for suc- 

 cessful explora- 

 tions, attractive to 

 the naturalist, and 

 especially the geologist, perhaps no locality within 

 easy distance can equal the Dorset coast, in that 

 part stretching from Studland and Swanage Bays 

 towards St. Alban's Head. With Mr. Gosse's 

 "Tenby," "Devonshire Coast," and invaluable 

 manuals, "Marine Zoology," as companions, much 

 accurate knowledge may be secured. At low water, 

 in pellucid pools, fringed with delicate algce of many 

 hues, and replete with quaint and curious forms, are 

 found specimens of the polyzoa, polypes inhabiting 

 cells, creatures allied to the moUusca, but living 

 under many strange and diverse forms and conditions. 

 In the class under consideration they are delicately 

 spread over, or commensal, on sea- weeds, shells, or 

 submerged substances, forming crusts, or attached as 

 minute plant-like tufts to rocks. Many of these 

 forms, so frondose is their appearance, appear, to 

 a casual observer, as minute plants. Upon closer 

 examination they are found to be horny, or calcareous 

 congeries of cells ; polypidoms, domiciles, in each a 

 polype, in a berth of its own, not only in association 

 and in intimate contact with countless neighbours. 

 No. 237. — September 1884. 



but individually aiding in, and contributing to, the 

 general construction and exquisite architecture of the 

 settlement. 



The solitary polype (Hydra), and its more beautiful 

 fresh-water allies, Lophopus, Plumatella, and Crista- 

 tella — the latter a community of individuals, with 

 power of locomotion, exhibiting a colony incessantly 

 seeking fresh pastures — are well known to every 

 possessor of a microscope. These forms are merely 

 imbedded in a gelatinous substratum ; they do not 

 found a permanent establishment in well-constructed 

 and castellated homes, but in the marine forms, with 

 some exceptions, the polype is discovered in a separate 

 lodgment of a substantial character, formed by its 

 capability of secreting carbonates of lime and other 

 substances, packing itself into a cavity, and by united 

 efforts forming an aggregated building, a general as- 

 sociation, a caucus. And these residences — polyzoaries 

 or polypidoms ("cells for retreat in danger") — are 

 varied in substance, form, and character. Space does 

 not admit the enumeration of all the varieties ; but 

 those most generally found, and typical, are horny 

 and flexible (Flustra), arborescent and plant-like 

 (Sertularia), stony and calcareous (Madrepores and 

 Corallines), filamentous and tubular (Anguinaria), 

 and greater varieties forming crusts on various sub- 

 stances, resulting in a pavement of cells. 



The subject of the plate, the dried polypidom of 

 Lcpralia nitida (?) (or verrucosa), of the family 

 Celleporidse, order Ascidioda (Johnston), is a congery 

 of such cells. From the mode of increase, there is 

 no limit to their number or security of preservation. 

 The polypes die, but the solid walls remain in accurate 

 connection with each other. New indiviiluals increase 

 at the margin. It appears that, when an original or 

 seminal cell is set up and completed, another begins 

 to form at its side. This process can be seen in the 

 Flustm; (Sea-mats), a common form, where round 

 the edge of the crust cells may be observed in every 

 stage ; some beginning, others half formed, and 

 many nearly completed. Although the polypidoms 

 of the order Ascidioda assume many diversities of 



