are frequently found covering wide 

 areas. The spines are generally green 

 in color, but in many varieties they are 

 of a rich purple. When highly magni- 

 fied these spines are seen to be strongly 

 ribbed. 



- One of the most interesting sights af- 

 forded by a marine aquarium is that of 

 a Sea Urchin turning over when placed 

 upon its back. This is accomplished as 

 follows : First, a few of the feet of the 

 back are thrust out and these cautiously 

 move about, reaching for some solid body 

 to which they may attach themselves. 

 When they come in contact with the floor 

 of the aquarium they immediately attach 

 themselves to it and pull the urchin a 

 little way over; additional feet are now 

 thrust out and attach themselves to the 

 floor. This process is continued until 

 the urchin has been literally pulled over 

 and placed right side up. 



It is a curious and significant fact that 

 in almost all branches of the animal king- 

 dom some species serve as food for man. 

 The Echinodea are no exception to the 

 rule and we find several species which 

 serve as food for savages and the poorer 

 classes of Europe and the West Indies. 

 The most important of these are the ed- 

 ible sea eggs of Europe ( Echinus esculen- 

 tus) and the edible Sea Urchin of Flor- 

 ida and the West Indies (Hipponoe escu- 

 lenta), which is figured on the plate. 

 They do not, however, form very dainty 

 articles of food, for Nature has expended 

 her taste upon the outward appearance 

 of the urchin and left little for the in- 

 terior. 



When a Sea Urchin is denuded of its 

 spines it presents a peculiar spherical or 

 rounded bodv studded over with knobs, 

 representing the balls which articulate with 

 the sockets at the base of the spines. The 

 species represented on the plate (Dia- 

 dema setosum) is a good example of a 

 denuded test or shell. In the center of 

 this shell may be seen the dark, sieve- 

 like madreporic body leading into the 

 stone. canal. Starting from the central 

 area, which is smooth, are the five rays 

 which are plainly marked by the double 

 rows of pores for the extension of the 

 ambulacral feet. Between the two lines 

 of pores the tubercles are small and sup- 

 port small spines, while on the outside 



the tubercles are very large and support 

 the larger spines. This species is an in- 

 habitant of Florida and the West Indies, 

 where it is very abundant. 



It is generally supposed that mar- 

 supials, like the kangaroo and the opos- 

 sum, are confined solely to the mam- 

 mals, but it is a peculiar and significant 

 fact that in nearly all branches of the 

 animal kingdom there is a small group of 

 species analogous to the marsupialia of 

 the mammalian class. The echinoids are 

 no exception to the rule and we find in 

 the cooler portions of the South Atlantic 

 Ocean several species of Sea Urchins 

 which develop in marsupia as truly as do 

 the young kangaroos in the pouch of 

 their mothers. In the genus Hemiaster, 

 which lives in the waters surrounding 

 the Kerguelen Island, the ambulacral 

 plates are depressed, expanded, or other- 

 wise modified to form four deep depres- 

 sions in the shell, the spines being so ar- 

 ranged as to form a more or less covered 

 passage from the ovarian opening to the 

 improvised marsupium. The eggs, which 

 are very small, scarcely more than a mil- 

 imetre in diameter, are passed along this 

 covered tube and laid in rows in the mar- 

 supium, where two^ spines keep each egg 

 in place. The embryos develop quite 

 rapidly and are between two and three 

 milimetres in diameter when they leave 

 the parent. Thus does Nature repeat 

 herself in her different creations. 



The sea eggs and sea porcupines are, 

 as a general rule, inhabitants of rocky 

 shores, while the flat urchins, like the 

 Sand Dollars and key-hole urchins, live 

 on sandy beaches in more or less shel- 

 tered bays, where they bury themselves in 

 the sand, either whollv or in part. One 

 may see the common Sand Dollar or sand 

 cake in San Diego Bay, California, bur- 

 ied to all depths and at every conceivable 

 angle, and packed so closely together that 

 one wonders how they are able to live in 

 such close proximity. 



In the Sand Dollar the shell test is re- 

 duced to extreme flatness and we wonder 

 how the animal finds room for itself in 

 such extremely narrow quarters. Not 

 only is the space narrow, but it is even 

 further curtailed by many partitions, 

 which radiate in fan-shape from a central 

 point and which connect the upper and 



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