Text-book of comparative anatomy . 96 COMPARATIVE ANATOMY CHAP. whole epithelium round this compound sensory organ, which is pro-tected in special indentations in the disc margin by lobes, is a sensoryepithelium with a thick nerve plexus. There are either 4 or 8, lessfrequently 12, 16, or even more rhopalia on the margin of theAcraspede umbrella. III. The sensory body at the aboral pole, so characteristic of theCtenopJwra, is a compound sensory organ of a very peculiar kind, which,according to its structure, is an auditory organ, or »ather, perhaps, anorgan for regulating the movement of the s
Text-book of comparative anatomy . 96 COMPARATIVE ANATOMY CHAP. whole epithelium round this compound sensory organ, which is pro-tected in special indentations in the disc margin by lobes, is a sensoryepithelium with a thick nerve plexus. There are either 4 or 8, lessfrequently 12, 16, or even more rhopalia on the margin of theAcraspede umbrella. III. The sensory body at the aboral pole, so characteristic of theCtenopJwra, is a compound sensory organ of a very peculiar kind, which,according to its structure, is an auditory organ, or »ather, perhaps, anorgan for regulating the movement of the swimming plates. The sensory body is constructed as follows. It consists at first ofa shallow pit-like depression between the 4 branches of the aboral. ec FIG. 73.—Sensory bodies of Nausithoe, after Hertwig (optical transverse section of the margin ofthe disc), sf, Sensory fold of the margin of the disc ; ec, ectoderm ; en, endoderm ; ga, gastro-canal; Jik, auditory body; o, otolith ; se, sensory epithelium ; oc, eye ; I, lens ; g, jelly. so-called funnel vessel. The ciliated body epithelium which formsthe base of this pit thickens considerably (Fig. 75, se). Its elementsare thread-like cells. In this sensory cushion are found depositsof pigment, which perhaps represent simple organs of sight. Eoundthe edge of the pit there rises a membrane which unites above in theshape of a bell, forming a sort of roof to the pit, which is thus trans-formed into a vesicle. The membrane is composed of the long ciliaat the edge of the pit cemented together. It is broken through byslits- at 6 places, and through these the sea water can freely reachthe interior of the vesicle. Two of these slits, which are oppositeeach other, belong to the median pla
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
