ACALEPH^E. 



ACALEPH^E. 



but De Blainville and MM. Chamisso and Eisenhardt coincide with 



Cuvier in believing that they are all referable to one, though the 



former admits that the fact is still 



somewhat doubtful. He observes 



that Bosc'a species, Holothuria 



appendicidata, (Porp&a (i/i/iendicu- 



lata, Lam.) was evidently established 



on an impaired animal. Eschscholtz, 



under the name of Porpita Midi/t/-- 



ranea, conjoins three of Lamarck's 



species, and describes three new 



ones, taking for his character the 



proportion of the cartilaginous TroBle ot Porpita ilaadtfera. 



disk, and especially that of the marginal cirrhi. 



Geographical l>istribution. Like that of Veldla, very wide. Bosc, 

 who met with them at sea, says the animal has the appearance of a 

 24-sous piece borne along by the waves. Examples, Porpita yiyantea, 

 and P. ylandifera. 



4. Polybrachionia. (Guilding). 



Dorsal support (austentaculuni) cartilaginous, naked, flattened, 

 rounded, radiated, concentrically striated; mantle (pallium) narrow, 

 free, surrounding the support; arms numerous, parallel, of various 

 lengths, elon- 

 gated, affixed 

 beneath, with 

 a power of 

 taking a de- 

 clining posi- 

 tion for the 

 purpose of 

 taking prey. 

 Mouth below, 

 central, purse- 

 shaped, exten- 

 sile. Tentacula 

 many, varying 

 in form, suc- 

 torial, cover- 

 ing the whole 

 ventral sur- 

 face. Eggs, 

 very email, 

 innumerable, 

 nestled among 

 the tentacnla. 

 Example, Pa- 

 lybrarhionia 

 Liunirnnii. 



This genus 

 has been esta- 

 blished by Mr. 

 (Juililing, who 

 describes the 

 support as 

 broad and 

 vitreous, the 

 body as ceru- 

 lean, the ten- 

 tacula as pal- 

 lid, and the 

 arms, which 

 are in a triple 

 series, "glandu- 

 luus, the glan- 

 dules being 

 pedunculated. 

 The diameter 

 of the mantle, 

 exclusive of 

 the arms, ia 

 stated to be 



eleven and a half lines. Mr. Guilding states that the animal is 

 wonderfully beautiful, swimming, or rather floating on the serene 

 surface of the Caribean Sea in calm weather, and embracing its prey 

 by the sudden downward application of some or all of its arms, 

 which are easily broken by attrition. 



We think there is hardly enough to warrant a generic separation in 

 this case; the species bears a strong resemblance to the Porpita 

 caeridea of Esehacholtz. Mr. Guilding observes that the Medusa 

 porpita of the 'Amamitates Academicae* seems nothing more than 

 the central disk of some species deprived of all the organs of the body. 



The fourth order is the PHTSOOBADJL. The structure of the 



creatures belonging to this order were but little known till the 



pulilii-atiou of Mr. Huxley's researches, in 'Philosophical Transac- 



for 1849. They are allied to the preceding order both in the 



matiiin of the gastric organs and in their means of locomotion. 



Tin- principal difference between this and the preceding families is, 



Polytrachioiiia Lmnaana, enlarged. 

 a, upper side j b, lower side. 



that we here lose the radiate form, and observe in the creatures which 

 belong to it a lateral symmetry. This order is now made to include 

 the genus Physalia and its allies, which are possessed of an air-bag, 

 by means of which they float through the ocean, and also the various 

 forms of Diphydce. These two forms were included by Cuvier in his 

 division of Hydrostatic A calephce. Before referring to their arrange- 

 ment, we shall give the principal results of Mr. Huxley's researches 

 into the anatomy of these creatures, as given by him in the 'Report of 

 the Twenty-First Meeting of the British Association for the Advance- 

 ment of Science.' We shall speak first of the Diphydw. If one of 

 these creatures is examined, it will be found to consist of two trans- 

 parent crystalline pieces, which look, when taken out of the water, 

 like morsels of cut-glass. One or both of these pieces contains a wide 

 cavity, lined with a muscular membrane, by the contraction of which 

 the animal is propelled through the water. The attachment of the 

 posterior piece to the anterior is very slight, and when detached it 

 will swim about independently for hours together. It was this cir- 

 cumstance which led Cuvier to suppose that the two pieces were two 

 independent animals, and in this he has been followed by the majo- 

 rity of zoologists. He describes the two individuals as always together, 

 one including itself in a hollow of the other (1'un s'emboitant dans 

 un creux de 1'autre), an arrangement which nevertheless permits their 

 separation without the destruction of life. They are, he observes, 

 gelatinous, transparent, and move very nearly like the Medmce. The 

 including individual (1'emboitant) produces from the bottom of its 

 hollow a chaplet (chapelet) which traverses a demi-canal of the inclu- 

 ded individual (1'embottd), and would seem to be composed of ovaries 

 and of tentacula and suckers like those of the preceding genera. 

 Cuvier then goes on to state the divisions established by MM. Quoy 

 and Gaimard, according to the relative forms and proportions of tho 

 two individuals. Thus in the JMphyes, properly so called, the two 

 individuals are nearly alike, pyramidal, and with some points round 

 their opening, which is at the base of the pyramid. In the Calpes, 

 the included individual has still the pyramidal form, but the inclu- 

 ding individual is very small and square. In the Abyles, the included 

 individual is oblong or oval, and the including rather smaller and bell- 

 shaped. In the Cubo'idcs, it is the included individual which is small and 

 bell-shaped ; the including individual is much larger and square. Ill 

 the Navicules, the included individual is bell-shaped ; the including 

 individual large also, but slipper-shaped (en forme de sabot). Cuvier 

 concludes by remarking that there are many other combinations. 

 There are two prominent forms of Diphydce, the Monogastric and the 

 Polygaitric. In the former a single polype is developed in a special 

 cavity of the anterior piece. In the polygastric a long chain of such 

 polypes, each enveloped in a little transparent bract, occupies a 

 similar position. These polypes have no oral tentacles ; but a long 

 thread-like tentacle, bearing lateral branches, which are terminated by 

 small sacs, is developed from the base of every polype. The small 

 prehensile sac has a peculiar form, but is only a dilatation of its 

 pedicle. It is much thickened on one side, and contains a great number 

 of the stinging hairs to which we have before alluded. The repro- 

 ductive organs are medusiform bodies, which are developed by 

 gemmation from the pedicle of the polype. 



In the Polijijastric lUphydce new polypes are continually being 

 produced by gemmation at the attached extremity of the polype- 

 chain, and in all the species the same gemmation is continually going 

 on among the prehensile and reproductive organs. 



The structure of the other forms of Phyaograda are modifications of 

 a common type, in the main identical with that of the Dipliydie. 

 The great difference is in the absence of the air-organ, or float. Tho 

 same continual multiplication of parts by germination goes on among 

 the Physsophoridie as among the Dipkydce, and the structure and 

 mode of development of the young organs are the same. Great variety 

 is presented by the reproductive organs, from the form of mere sacs 

 to that of free-swimming bodies precisely resembling Medusie, and 

 developing the generative elements only subsequently to their 

 liberation. In Phymlia, the female organs are free-swimming medusi- 

 form bodies, while the male organs are simply pyriform sacs. 



As a general conclusion it may be stated that the Physograda are 

 essentially composed of two membranes, an outer and an inner, which 

 are called by Mr. Huxley ' foundation membranes," since every organ 

 is formed by the modelling into shape of one or other or both of these ; 

 commencing as a simple process, or diverticulum, and assuming its 

 perfect form by a gradual change of development. The stomach has 

 no walls distinct from those of the general varieties. The reproductive 

 organs are always developed externally. The stinging hairs, or thread- 

 cells, are found in all the species in the greatest abundance. 



The following is the arrangement of these creatures according to 

 M. de Blainville : 



PHYSOGRADA. 



* 



Natatory organ simple and lamellar, 



1. Physalia. 



Generic Character. Body oval, rather elongated, more narrow and 

 proboscidiform anteriorly, hydatiform in the middle, attenuated and 

 obtuse posteriorly ; mouth star-shaped and terminal ; anus lateral ; 

 a foot in form of a crest or oblique lamina, directed from before 



