ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 525 



foot-suckers, of the skin, of the muscles, of the nerves to the closing muscu- 

 lature of the cloaca, and of those to the mesentery of the hinder end of 

 the body. In the third j^lace there are sensory or terminal organs. The 

 tentacular nerves serve the sensory plates of the tentacles of the Aspido- 

 and Dendrochirota, the bud-like sensory organs, and the tactile papillte 

 of the tentacles of the Synaptidee. The sensory cells of the skin are 

 innervated by the tegumentary nerves ; those of the foot-suckers and 

 ambulacral papillas by the nerves that go to them, while the tegumentary 

 nerves supply the tactile papillae of the skin of the Synaptidae and the 

 sensory cells of the skin. When auditory vesicles are present the radial 

 nerves give off auditory trunks. 



Anatomy of Ophiuroids and Crinoids.* — Dr. 0. Haraann continues 

 his account of the morphology of Echinoderms by treating of the 

 anatomy of Ophiuroids and Crinoids. In summarizing his results 

 generally he commences with the ambulacral nervous system ; this is 

 found in all Echinoderms, lying, iu Asterids and Crinoids, always in the 

 ectoderm, and in others in the cutis, where it is generally surrounded by 

 schizocoel spaces. In Crinoids the oesophageal ring is lost. The facts 

 that the ambulacral nerve-trunks of Ophiuroids are jointed, and that 

 there are ganglia in the dorsal as well as the ventral cells, are of great 

 importance. The ambulacral and mesodermal nervous system of the 

 Crinoids and its origin are next considered. This system consists of a 

 mesodermal pentagonal nerve-ring, and, in each arm, of two longitudinal 

 nerves, and the question arises, did these parts arise separately or is 

 their present condition a secondary one ? The oral-mesodermal jjortion 

 is regarded as being derived from the ambulacral nervous system of 

 Crinoids, support for this view being found in the fact that the latter is 

 only preserved in rudiment in the epithelium ; this ambulacral system 

 has no central organ, and the nerves in the epithelium are very poorly 

 developed as compared with the homologous nerves of other Echinoderms. 

 The ectodermal portion, therefore, has passed from the ectoderm into 

 the mesoderm, and its branches have been developed in the same way as 

 the peculiar nerves of Ophiurids, which arise at definite intervals from 

 the ambulacral nerves and form intervertebral nerve-branches. But 

 while the latter have retained connection with their point of origin, they 

 have lost it in the Crinoids. Further evidence in support of this view 

 is given by the agreement in structure which the three parts present. 

 In all three there are the same nerve-fibrils and ganglionic cells. "While 

 there is no direct connection between the ej)ithelial, ambulacral nervous 

 system and the other parts, there is such between the dorsal and ventral 

 portions. 



The peripheral nervous system and the sensory organs are next 

 considered ; in the Crinoids there are norve-endings in the epithelium 

 of the skin similar to those found in Asterids and Holothurians, as also 

 the sensory buds on the tentacles, which have been recognized by Jickeli 

 as sense-organs. In the Ophiurids, as the physiological investigations 

 of Preyer have conclusively shown, the peripheral nervous system is 

 exceedingly well developed; special sensory organs may be found in 

 large numbers on the tentacles of Oj)hioihrix, and the nerve-endings in 

 the epithelium are similar to those of Crinoids. In all groups there is 

 a nervous system in the epithelium of the enteric tract. 



* Jenaische Zeitschr. f. Naturwiss., xxiii. (1889) pp. 233-388 (12 pis.). 

 1889. 2 



