NATURE 



413 



THURSDAY, MARCH 4, 1880 



THE MEDUSA 

 Das System der Mcdusen ; erster Theil einer Monographic 

 der Medusen. Von Dr. Ernst Haeckel, Professor an 

 der Universitat Jena. (Jena: Gustav Fischer, 1879.) 



THIS is one of the most beautiful books which the 

 science of zoology, which is rich in beautiful books, 

 can boast of. The Medusa* are the most graceful, 

 delicate, exquisitely formed and withal the most rare and 

 inaccessible of living things. No inlander has any notion 

 of what these tender, translucent beings can show in the 

 way of colour, symmetry, and rhythmic movement. They 

 cannot be carried to distant aquaria — but live only in the 

 clearest, brightest parts of the sea at some distance from 

 the coast. No system of pickling fluids is known which 

 can keep them for us undistorted. To study them, even 

 to see them at all as they are, the naturalist must betake 

 himself to the coast and in calm weather sweep the 

 surface of the sea with his towing-net, much as the insect- 

 man sweeps the hedge-rows. Many and some very lovely 

 forms occur on our own coast — but our capricious climate 

 renders it always uncertain when or where any of the 

 Medusae may be found, sensitive as they are to every 

 change in the movement of the waters, and sinking far 

 out of reach in certain states of weather. The Mediter- 

 ranean, with its more genial atmosphere and sheltered 

 bays, has always furnished naturalists with the richest 

 supply of pelagic animals, whilst even the mid-ocean is 

 more favourable as a hunting-ground for them than our 

 ever-restless Channel and North Sea. 



The term Medusa dates from the time of Linnaeus. 

 Peron and Lesueur and after them Eschscholtz were the 

 first naturalists who devoted monographs to the Medusae, 

 and valuable as was their work it contained descriptions 

 of only some dozen genera and species (1829). After a 

 long interval (1848) Edward Forbes, who was attracted 

 by the symmetrical forms and delicate contours of these 

 animals as he was by the more rigid and less beautiful 

 starfishes, published his monograph of the naked-eyed 

 Medusae (Ray Society). After him we have, amongst 

 others, the valuable anatomical investigations of Gegenbaur 

 (Zeitschr. fiir wiss. Zoologie, 1857), and the important 

 treatises of the two Agassizs, father and son (Louis 

 Agassiz, " Contributions to the Nat. Hist, of the United 

 States," 185762 ; Alex. Agassiz, " Catalogue of Acalephae," 

 1865). Still later we have the magnificent volumes of 

 another artist-naturalist — Prof. Allman — who shows in 

 every line of his pencil how keenly he appreciates the 

 grace and elegance of the hydroid polyps and their 

 medusa-offspring, to which his two large volumes are 

 devoted (Ray Society, 187 1). Allman's treatise more 

 especially aims at giving an account of the naked hydri- 

 form polyps and the medusae which are produced like 

 fruit upon their branches, separating and swimming away 

 in many instances as free independent creatures, though 

 sometimes aborted and fixed as sporosacs. Ernst Haeckel, 

 on the other hand, has not proposed to himself to trace 

 the individual life-history of the Medusae. He takes them 

 as he finds them, and whilst giving us in this first part 

 alone twenty quarto plates of drawings mostly from the 

 Vol. xxi. — No. 540 



life, exposes their agreements and variations of structure 

 in the most masterly, exhaustive, and logically conceived 

 treatise which it has been our lot to encounter in zoological 

 literature. The symmetry and precision which Haeckel 

 is able to exhibit in his systematic discussion of the 

 Medusas is no doubt in large degree attributable to the 

 isolated and strongly marked character of the natural 

 group which they form ; it is however also in no small 

 measure due to the exhaustive knowledge of their struc- 

 ture which his own researches spread over some twenty 

 years, and more recently those of his pupils, the brothers 

 Hertwig have brought together. 



There are very few if any groups of animals so extensive 

 in distinguishable variety of form, the detailed anatomy 

 of which is so well known as is now that of the Medusae, 

 Hence the thoroughly satisfactory character of the syste- 

 matic classification of them which is possible. 



Unfortunately the life-history of a large number of 

 Medusae is not so well known, and probably for a long 

 time will not be known. It is a fact familiar to even 

 the least profound student of zoology, that whilst some 

 medusae are produced by budding from colonies of 

 hydriform polyps and give rise by their eggs to such 

 hydriform colonies which again produce these sexual 

 medusa-forms by budding, yet other medusae develop 

 directly from the egg of a parent medusa into young 

 medusae without ever having anything to do with hydri- 

 form colonies or " persons." This interposition of a 

 hydriform stage and an act of fissiparous generation 

 appears to have little if any relation to the varieties of 

 structure presented by medusae. Medusas closely allied 

 may some have hydriform young and others not. On the 

 other hand the hydriform polyps exhibit the same kind 

 of irregularity in their proceedings, some species pro- 

 ducing the neatest of medusas which swim away to carry 

 their seed far and wide, whilst closely similar species 

 produce not free- swimming elegant medusae but aborted 

 wart-like knobs (sporosacs), evidently the degenerate 

 representatives of medusae ; and these, without being 

 detached, develop the eggs and the sperm from which a 

 new generation of hydra-forms will spring. 



Clearly, then, there was room for a treatise on the 

 Medusae which should, without waiting for the long 

 process of growth of knowledge, ignore the hydriform 

 phase, just as the admirable monograph of Allman treats 

 of the hydra-forms (of a limited group) without touching 

 those medusae not yet traced to hydriform parentage. 



It appears that in certain large outlines a classification 

 is possible which shall hit off simultaneously the relation- 

 ships of both medusa-forms and their respective hydra- 

 forms. But that this should extend into the details of 

 small groups, such as families and genera, is not to be 

 expected. Beyond a certain limit the Medusas and their 

 parentally related hydra-forms do not vary concomitantly 

 A systematic and exhaustive treatise on Medusae, as 

 such, was then, we would insist, a great want. No one 

 but the most energetic and industrious of men endowed 

 with the greatest skill as a draughtsman and devoting 

 himself for years to work on such coasts as those of the 

 North Sea, Bay of Biscay, Adriatic, Mediterranean, and 

 Red Sea, such a man as we have in Prof. Ernst Haeckel, 

 could have produced the desired treatise. Besides living 

 specimens, Haeckel has studied those received in alcohol 



