. Zoology : for students and general readers . Zoology. Fig. 80.—Schematic figures of a Sea-urchin. A, from the oral end ; B, from one pide. Ambulacra indicated by rows of dots, r, ambulacra]; ir, uiterambulacral areas; o, mouth; a, vent.—After Gegenbaur. In order to examine the external anatomy, the shell should be deprived of its spines in part, meanwhile observ- ing the mode of attachirtent of the spines, of which micro- scoiDic sections should be made. The solid mouth- parts, the oral membrane sur- rounding the five sharp conical teeth or "pyramids," and their mode of attachment
. Zoology : for students and general readers . Zoology. Fig. 80.—Schematic figures of a Sea-urchin. A, from the oral end ; B, from one pide. Ambulacra indicated by rows of dots, r, ambulacra]; ir, uiterambulacral areas; o, mouth; a, vent.—After Gegenbaur. In order to examine the external anatomy, the shell should be deprived of its spines in part, meanwhile observ- ing the mode of attachirtent of the spines, of which micro- scoiDic sections should be made. The solid mouth- parts, the oral membrane sur- rounding the five sharp conical teeth or "pyramids," and their mode of attachment to the " auricles " in the shell, should be thoroughly investigated, as well as their re- lations to the mouth-opening and the digestive canal. The shell is a flattened sphere, consisting of ambulacral plates, perforated for the exit of the feet, and a broader series of five rows of interambulaei-al j)lates to which the spines are attached, and of sucb form and ari-angement as to give the greatest possible strength and lightness to the shell (Figs. 80, 81, 82). The outlet of the alimentary canal is situated on the aboral (abactinal) or upper end of the shell, while the madre- poric plate is situated upon the top or end of the shell (as the animal moves mouth downward), being a modifica- tion of one of the genital plates (Pig. 81, m). There are five large plates, one at each end of the interambulacral zones meeting on the aboral end of the body ; in them are the ovarian openings through which the eggs escape ; these. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Packard, A. S. (Alpheus Spring), 1839-1905. New York : Henry Holt
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
