The porifera and coelentera . The space between the stomodaeum, gastrovascular sy.^tem,and body walls is occupied by a gelatinoid substance, in which areimbedded numerous muscle fibres, whose structure and arrange-ment will be described further on. The sensory organ at the aboral pole consists of a shallow de-pression of the ectoderm, lined by a modified and probably sensoryepithelium. Within many of the epithelial cells are formed cal- THE CTENOPHORA careous sphaeroids (otoliths); and, according to Samassa (21),when the otoliths are fully formed, they are ejected, still sur-rounded by the rem
The porifera and coelentera . The space between the stomodaeum, gastrovascular sy.^tem,and body walls is occupied by a gelatinoid substance, in which areimbedded numerous muscle fibres, whose structure and arrange-ment will be described further on. The sensory organ at the aboral pole consists of a shallow de-pression of the ectoderm, lined by a modified and probably sensoryepithelium. Within many of the epithelial cells are formed cal- THE CTENOPHORA careous sphaeroids (otoliths); and, according to Samassa (21),when the otoliths are fully formed, they are ejected, still sur-rounded by the remnants of the cells in which they were formed,and become aggregated together to form a mul1)erry-like otolith mass is supported by four balancers, delicate lamellaeof peculiar shape formed by fused cilia. The whole structure,sensory pit and otolith mass, is covered over and protectedby a transparent doine formed by fused cilia (see Fig. II. 1, 2).The four balancers lie in the angles of intersection of the sagittal and. **^«iiggis£ Fig. II. 1.—Surface view of tlie .sense organ of Horniiphnrn plumosa. Pf, polar fields; a, ampullae ;xji, excretory pores ; r, groups of gland cells ; cf, ciliated furrows. (After Cluin.)2.—The same seen from the side, ot, otolith mass ; cu, cupule formed of fused cilia. transverse planes; from the base of each of them two rows of ciliatedfurrows run outwards to end in the uppermost comb of each sensory pit is produced on either side, in the sagittal plane,into an elongated band-like ciliated tract. These tracts areknown as the polar fields (Fig. I. 4, and Fig. II. 1, If), and itwas supposed that they served as olfactory organs, but Samassa(21) states that they are nothing more than tracts of simpleciliated epithelium, devoid of sensory cells, so their function re-mains unknown. Samassa denies the existence of any nervousstructures beyond those already mentioned; but Hertwig (13),whose observations have recently been confirmed
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
