P O L Y C Y S T I ]^ S . 



PREFACE TO FIRST EDITION 



"But what are Polycystins" is the constant exclamation. — So little is yet known of these 

 curious organisms that naturalists have not yet decided on their exact place. They belong 

 however, to the sub-kingdom "Protozoa," and Mr. Reay Gi*eene in his "Manual" places them 

 between "Rhizopoda" (of which the tyj^e is Amceba, so commonly found in fresh water as little 

 gelatinous lumps, of the very lowest form of animal life) and Sponges, which form flinty 

 interior skeletons, called spicules, to support the spongiose web, and the animal mass of jelly, 

 called Sarcode, with which they are invested. The Polycystins are also masses of Sarcode, but 

 they appear to form both internal spicular-hke supports radiating from the nucleus, and also 

 external shells of a network of flint, through the interstices of which they are said to protrude 

 pseudopodian threads (pei-haps analogous to the tentacles of Sea-anemones and Star-fishes or 

 arms of Hydra) by means of which they are supposed to imbibe nourishment, and to have some 

 powers of locomotion. A careful observation of the larval changes of the Echinoderms, and 

 the pupae states of other young things, can make one understand how the protean forms of the 

 Polycystins need not all designate distinct species, but that many grotesque differences of 

 shape, and of spinous ornamentation may, in reahty belong to the same object, in different 

 stages or under different circumstances of development, such as more or less pressure, abundance 

 or scarcity of the siliceous material in the surrounding water, &c. Perhaps there may be said 

 to be four classes of form : — 1st., the discoidal or planorbian flattened spheres, variously 

 winged or bordered; 2nd., the orbicular, "with or without spines; 3rd., the vase or bell-shaped 

 consisting often of repeated globes growing out of each other, sometimes with a re-duphcation 

 of parts, that might seem to indicate a tendency towards increase by fission ; 4th., the plane or 

 straight-sided forms. 



Dr. Wallich promises a full history of the structure and mode of development of Polycystins 

 in his forthcoming work, having obtained living specimens in his recent deep-sea soundings : 

 some in association with those wondrous benighted star-fishes from two miles deep. 



Professor Johannes Miiller fished them up frequently in the Mediterranean, near Cette and 

 St. Tropez ; always from great depths, and under very clear pure sea-water, but from their 



