461 



ECHINARACHARIAS. 



ECHINID^E. 



462 



watched, or it will certainly go overboard. It is absolutely necessary 

 that the eggs on which it is fed during the voyage should be as fresh 

 as possible : they can be preserved in lime-water. If milk is not to 

 be procured, water must be supplied daily ; and egg and liver, or 

 fresh meat, cut small, should be given at least every alternate day. 

 When the weather will permit, it should be fed once a day. Half an 

 egg, boiled hard, and the liver of a fowl or other bird, will suffice for 

 a meal. The animal should be kept warm, and should be well sup- 

 plied with clean straw. It will be as well to nail two or three pieces 

 of wood (battens) across the floor of the cage, to prevent the animal 

 from slipping about when the ship is unsteady. ('ZooL Proc.,' 1834, 

 Part 2.) 



It inhabits the Blue Mountains, &c., the environs of Port Jackson, 

 and Van Diemen's Land. 



ECHINARACHARIAS. [EcHTNic*.] 



ECHINASTR^EA. [MNADREFHYLLKEA.] 



ECHI'NID^E, a family of Radiated Animals, comprehending those 

 marine animals popularly known by the name of Sea-Eggs, or Sea- 

 Urchins (Oursins of the French). 



De Blainville makes the Echinidea, the second order of the class 

 Echinodermata, and he thus defines the order : 



Body oval or circular, regular, sustained by a solid shell, which is 

 calcareous and composed of polygonal plates, disposed in radiated 

 order in 20 rows, which are either equal, or alternately and regularly 

 unequal. The shell supports upon proportionable mamillary projec- 

 tions stiff spines which are extremely variable in form, and is pierced by 

 a series of pores, forming by their assemblage a kind of ambulacra. It 

 radiates more or less regularly from the summit to the base, and gives 

 exit to tentaculiform cirrhi. Mouth armed or unarmed, pierced in a 

 notch of the shell invariably on the lower side. Vent always distinct, 

 but offering many variations in its position. Generative orifices four 

 or five in number, disposed round the dorsal summit. 



The Sea-Urchins are a family of considerable interest both to the 

 zoologist and geologist. To the first they offer the most perfect 

 examples of the type of radiate animals, whilst their hard covering 

 and habits of living in the sand, have preserved them in many rocks 

 of the strata of the earth for the study of the geologist. They are 

 distinguished from the other Echinodermata by their form, which is 

 more or less rounded without arms of any kind. Calcareous matter 

 ia deposited within their integument so as to form a series of regular 

 plates, which are studded with tubercles, bearing jointed on them 

 spines of various forms and sizes according to the genus or family. 

 These spines are sometimes small in proportion to the size of the 

 body, but in others they are singularly large, and excite wonder as to 

 how they can be employed by the animal. These spines have a 

 beautiful microscopic structure, being composed of cells which are 

 arranged around a common centre, almost in the same manner as the 

 zones of wood in a tree. (Carpenter ' On the Structure of Shells.' ) As 

 in other Echinodermata, the Sea-Eggs have ambulacra variously 

 arranged, perforated with pores for the exsertion of suckers, or 

 feet. The ovarian holes are seated on the apex, whence the eggs are 

 extruded. There are two openings for the digestive apparatus a 

 mouth, always placed below and sometimes connected with an internal 

 dental apparatus, and a vent, which is very variable in its position. 

 The intestine is winding, and is attached to the inner surface of the 

 shell by a mesentery, the surface of which, as well as of the membrane, 

 lining the shell, is covered with vibratile cilia, and undoubtedly 

 serves for respiratory purposes. The ovaries are placed in the spaces 

 between the ambulacra. The vascular system is more or less 

 complicated, having a portion with muscular parietes, and exhi- 

 biting pulsations. Van Beueden has asserted the existence of a 

 nervous system in the Echinida;, but no one has yet confirmed his 

 observation. 



The Sea-Urchins progress by means of the joint action of their 

 suckers and spines. Many of them moor themselves also by means 

 of suckers, and thus adhere firmly to the rocks. Professor Agassiz 

 denies that they adhere by means of their suckers, or that these 

 organs serve the purposes of progression. This is however opposed 

 to the observations of the majority of naturalists, and Professor E. 

 Forbes refers especially to this point for the purpose of giving his 

 unqualified opposition to the assertion of Professor Agassiz. As to 

 what uses these organs are applied to, if not for progression, Professor 

 Agassiz states that " we are yet unable to solve." 



The Sea-Urchins are free throughout their existence, unlike the 

 Attcriadfx, in which we find a fixed condition in the earliest periods of 

 their development. [ECHIUODERMATA.] 



With regard to the classification of the Echinida;, Professor E. 

 Forbes remarks that there has been " a tendency to an extreme multi- 

 plication of genera." 



Breyn, Klein, Linnams, Leske, Lamarck, Cuvicr, Gray, Desmarest, 

 Goldfuss, Von Buch, Desmoulins, Agassiz, and E. Forbes, are the 

 principal zoologists who have undertaken the classification of the 

 I-,: hi a"!, i. De Blainville observes that the relative position of the 

 month and the vent, and above all, of the ambulacra, are the prin- 

 cipal point* on which most of these writers have rested ; and as he 

 considers that this mode of viewing the subject has led to approxima- 

 tions not very natural, he proposes a system based on the following 

 grounds ; 



1st. On the general form of the body of the animal, which, at first 

 subradiated, becomes by little and little completely radiated in all 

 the parts which constitute it. 



2nd. Upon the position of the mouth, which, nearly terminal and 

 transverse, or bilabiated, in the first species, becomes completely 

 central and circular in the last. 



3rd. On the arming of this mouth, which, completely null in a 

 great proportion of the Echinidce, is, on the contrary, very powerful 

 in the rest. 



4th. Finally, on the position of the vent, on the number of ovaries 

 and their orifices, on the nature of the spines and the tubercles 

 which support them, as well as on the disposition of the ambu- 

 lacra. 



Synoptical Table of the Genera, according to De Blainville : 



Subterminal . . f Spatangus. 



\ Ananchites. 



Nucleolites. 



Echinodypeus. 



Echinolampas . 



Cassidula. 



Fibularia. 



Echinoneus. 



Mouth . 



Subcentral . 



Without teeth . . 



Central; Vent. .. 



! Echinocyamua 



Laganui. 

 Armed with teeth . . < Clypeatter. 



Echinodiicus. 



[ Scutella. 



( Infra-lateral Galerites. 



f Echinometra. 



I Central < Echinus. 



\_ Gidaris, 

 Sub-Family 1. Excentrostomata. 



Spatangus. Body oval, more or less elongated, heart-shaped, wider 

 before than behind, with a furrow more or less profound at the 

 anterior extremity. Shell delicate, of little solidity, composed of 

 large polygonal plates, not many La number. Spines short, flat, sessile, 

 and scattered. Ambulacra incomplete, only four in number. Buccal 

 notch more or less anterior, transverse, bilabiated, circumscribing a 

 mouth without teeth. Vent terminal, and rather above than below 

 the border. Genital pores four in number, disposed in two pairs. 

 The species are very numerous, and are subdivided by De Blainville 

 and others into sections according to their shape, &c. The following 

 is De Blainville's method : 



o. Species whose ambulacra are not petaloid, and form scarcely 

 but two lines, a little broken or bent at their internal side, and 

 which have a rather deep anterior furrow, and the mouth not much 

 in front. 



S. arcuarius of Lamarck, the Common Heart-Urchin, may be taken 

 as an example of this section. It is the S. pusillus of Leske ; S. 

 cordatui, Fleming; S.flavescens, Miiller; Echinus spatangus, Linnaeus; 

 E. pmillue, Gmelin; E, cordatus, Pennant; Amphidotus pusillus, 

 Agassiz. It is the commonest form of Spalangus in the European 

 seas. It abounds in all the bays of Great Britain, and after storms 

 is cast on shore. Popularly it is called in England the Mermaid's- 

 Head, the Child's-Head Urchin, the Hairy Sea-Egg. 



0. Heart-shaped species, with five deep and straight dorsal furrows, 

 in which the ambulacra are hidden. Ex. S. Atropos. 



y. Species whose ambulacra are petaloid, going from a centre, 

 and which have an antero-dorsal furrow more or less deep, occupying 

 the place of the fifth ambulacrum ; the posterior pair shorter than 

 the anterior. This section is divided into sub-sections, according to 

 the depth of the ambulacra. 



S. pnrpurem, the Purple Heart-Urchin, is an example of this 

 section. It is found in the seas of Great Britain, and is one of the 

 handsomest species of the whole family. It grows to the length of 

 4 inches by 3J inches broad. It is of a deep purple colour, with pale 

 spines ; some of the spines are very long and curved. 



8. Species whose anterior furrow is much less deep, or nearly null, 

 and whose ambulacra, more or less petaloid, to the number of four, 

 occupy the greatest part of a sort of dorsal plate, circumscribed by 

 a sinuous line without tubercles or spines. This section includes the 

 genus Brissus of Klein. 



B. lyrifer (Forbes), the Fiddle Heart-Urchin, is a British species, and 

 may be taken as an example of the section. This species has been taken 

 by Professor E. Forbes in various localities in the testuary of the 

 Clyde, off the island of Cumbury in Rothsay Bay and the Kyles of 

 Bute. It is a handsome and remarkable species. It has a red body 

 with pale yellowish-white spines, and the dorsal and post-anal 

 impressions of a rich brownish-purple. It inhabits mud at the depth 

 of from 10 to 15 fathoms. 



. Heart-shaped species, rather strongly widened and notched in 

 front, with five distinct and truncated ambulacra. Ex. & gibbus. 



(. Species whose anterior furrow is still distinct ; whose ambulacra, 

 to the number of four, are marginal, and sometimes complete, or 

 reaching up to the mouth ; and whose genital pores are five. This 



