414 



NATURE 



[Marc A 4, 1880 



from all parts of the world, including some collected by 

 the Challenger. 



We could wish some of our readers who may know 

 Ernst Haeckel only as the populariser of Darwinism and 

 the opponent of Virchow's proposal to establish a scientific 

 popery, to go through the work which he has just pro- 

 duced. Much as we value Haeckel's speculations and 

 his championship of free science, we are ready to admit 

 that in such work as the present he is seen at his best. 

 Speculation and polemics are here far out of sight indeed 

 — the work is of the most solid and genuine character. 

 Page after page is devoted to the systematising and 

 exposition of an immense mass of facts — facts as hard 

 and stubborn as any anti-theorist could wish — yet to a 

 large extent new or little considered hitherto, and at the 

 same time as beautiful and fascinating as any region of 

 nature to which the naturalist can turn his attention. 



A medusa may be compared in form to an umbrella, a 

 mushroom, or a clapper-bell. This does not suggest the 

 most beautiful set of objects ; it is, however, our own 

 fault if we do not finish off our umbrellas and bells with 

 the same elegance which characterises the medusa. The 

 handle of the umbrella, stalk of the mushroom, or clapper 

 of the bell is sometimes quite short and broad, sometimes 

 very long, reaching far away beyond the disk, dome, or 

 bell from which it hangs. It is known as the manubrium, 

 whilst the expanded disk is called the umbrella. The 

 manubrium is hollow and leads up into a wide cavity in 

 the disk, which originally extended right up to its margin, 

 but by the concrescence of its walls is reduced to four or 

 more radiating pouches or canals and a marginal circular 

 canal. The edge of the disk has longer or shorter hollow 

 tentacles (rarely solid) depending from it, and these vary 

 to any extent in the different kinds of medusa; as to their 

 number (from one to some hundreds) and length. The 

 shape of the umbrella is either flat or more or less elevated 

 until it may be quite like an oriental bell or even globular. 

 Besides tentacles we may find on the margin of the disk 

 three kinds of sense-organs, simple eye-spots, simple 

 auditory sacs, or lastly, what I have elsewhere termed 

 " tentaculocysts," modified tentacles which act as auditory 

 organs and have often eye-spots on them as well. 



The generative organs (spermaries and ovaries) are 

 usually in separate individuals, and are placed either in 

 the walls of the manubrium or in the walls of the radiating 

 canals or pouches of the disk. All the parts of the disk 

 and manubrium are arranged as radii around a common 

 axis. The first four radii to appear in the course of the 

 growth from a simpler phase of development are called 

 the per-radii, the next four (between these) the inter-radii, 

 the next eight between these the adradii. An organ (lobe, 

 tentacle, canal, or sense-organ) may be therefore per- 

 radial, inter-radial, or adradial in position. The whole 

 of this symmetrically arranged structure is usually of 

 glass-like appearance, yet with some exceptions quite 

 soft and gelatinous. Often the canals, eyes, and genera- 

 tive bodies are picked out with brilliant colour, red or 

 orange, or of a more delicate pink or blue. 



1 he large variety of medusae now known, amounting to 

 many hundred species, are divided primarily into two 

 great groups, the Hydromedusa: and the Scyphomedusae. 

 Prut. Haeckel uses Gegenbaur's terms for these, viz., 

 Craspedotae and Acraspeds. Eschscholtz and Forbes 



had long ago sought for characters by which to define 

 these two large groups. The Hydromedusa; never as 

 medusas nor in their hydriform phase possess gastral 

 filaments or phacellae, they always (?) develop their 

 generative organs from the superficial cell-layer known as 

 ectoderm, as shown by Haeckel's pupils, the Hertwigs, 

 and at the margin of the umbrella they always present a 

 delicate in-turned rim, the velum, which is muscular and 

 not penetrated by canals. Further, whenever they do not 

 develop directly from the egg of a parent medusa but 

 pass through a hydriform phase — the polyps are of the 

 shape and character known as hydroids or hydrae. On 

 the other hand the Scyphomedusae always possess gastral 

 filaments or phacellae, which are tufts of tentacle-like 

 processes placed in four groups inter-radially on the oral 

 floor of the stomach, where it widens out in the umbrella; 

 they always develop their generative organs from the 

 deep cell-layer known as endoderm, and they never have 

 at the margin of the umbrella a true velum, though one 

 (Charybdaea) has a membranous inturned rim which is 

 very like the velum of Hydromedusa; but penetrated by 

 vessels (as shown by Claus). Further the sense-organs 

 of Scyphomedusae are always tentaculocysts (though these 

 occur also in one group of the Hydromedusa;), and when- 

 ever the hydriform phase is exhibited in development 

 from the egg, the polyp is not a " hydra " but a " scyphi- 

 stoma," with broad disk-like body, and gives rise to 

 medusa; not by budding (as in Hydromedusa;) but by 

 transverse fission. 



The Scyphomedusa; (Acraspeda; of Gegenbaur) are 

 deferred by Prof. Haeckel for another volume ; they 

 comprise the large jelly-fish Aurelia, Rhizostoma, Cyanaea, 

 and such forms, as also the very beautiful and interesting 

 Charybdaea, and the Lucernarias, these last being forms 

 which combine the characters of polyp and jelly-fish, for 

 they can both fix themselves by a foot -like process of the 

 aboral pole of the umbrella, or loosen their hold and 

 swim the other way up as a medusa. Though medusae 

 usually swim mouth downwards, yet it is quite common 

 for them to swim sideways or to float mouth uppermost 

 or even to rest on the sea-bottom in that position. 



It is to the " Legion " Hydromedusa; that Prof. 

 Haeckel's first volume and twenty plates are devoted. 

 He divides them into two sub-legions — the Leptolinae 

 and the Trachylinae — in each of which are two orders 

 parallel to one another. The Leptolinas are Hydro- 

 medusa;, with soft and mobile, originally hollow tentacles ; 

 with ECTOdermal otolith cells, usually budded from 

 a hydriform colony. The Trachylinae have hard and stiff, 

 originally solid tentacles with ENDOdermal otolith cells 

 (belonging to tentaculocysts), and, as far as is known, 

 develop direct from the egg. The Leptolinas contain the 

 orders Anthomedusa; and Leptomedusa; ; the Trachylinae 

 contain the orders Trachomedusa; and Narcomedusae. 

 One order from each sub-legion, the Anthomedusae 

 and the Narcomedusae, is characterised by having its 

 generative organs placed in the wall of the manubrium ; 

 whilst the other order in each sub-legion is characterised 

 by having these organs placed in the course of the 

 radiating canals. 



The Anthomedusae are further characterised by never 

 having otocysts or auditory organs at all, but always 

 marginal eye-spots. Their tentacles may be simple, 



