ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 63 



the absolute impossibility of completely separating the nervous from 

 the surrounding tissues, and consequently, of being always certain as 

 to the truly nervous character of the fibres and cells which he had 

 under examination. 



A transverse section of a radial nerve showed that the periphery 

 was surrounded by cells, several layers thick, and that in the Aspido- 

 chirotae, there were distinct aggregations of cells right and left of the 

 middle line ; these bands were not seen in the Dendrochirotse or in 

 the Synaptidae. Internally one sees here and there cells, which in the 

 Aspidochirotge exhibit a certain arrangement, and which may be dis- 

 tinguished as internal and marginal ; histologically, these cells have 

 the same structure — a relatively large nucleus and a small quantity 

 of protoplasm. The nervous band is provided with a membranous 

 sheath which extends along its whole length and divides it into two 

 halves ; it is traversed by a system of transverse as well as of longi- 

 tudinal fibres. The former may be certainly believed to enter into 

 connection with the nerve-cells, but the relations, and indeed the 

 essential nature, of the latter require further investigation. 



Some remarks are made on the sensory organs, but no close 

 examination has yet been made of the structures at the base of the 

 tentacles of Synapta, which Miiller regarded as eye-spots, or the 

 auditory organ of Baur. The author has discovered at the end of the 

 ambulacral pedicels and of the tentacles, plates which appear to have a 

 fine tactile sensibility. 



Vascular System of Echinoderms.* — In No. VI. of his ' Notes 

 on Echinoderm Morphology,' P. H. Carpenter discusses the recent 

 utterances of various French anatomists on the anatomical relations 

 of the vascular system. 



Attention is first directed to the researches of Koehler, who finds, 

 in addition to the one vascular ring round the mouth of an Echinus 

 which has been acknowledged by Hoffmann and by Perrier, another 

 oval ring which can be injected by inserting the cannula into the 

 lower end of the "heart" or "ovoid gland" through the intermediation 

 of a vessel which lies beside but is quite distinct from the water-tube. 

 The injection will pass also into ramifications within the Polian 

 vesicles, and, if pressure be used, into these organs, while the water- 

 tube and radial vessels will also be injected. In Spatangids either 

 of the two oral rings may be injected from the corresponding radial 

 vessel, and each ring sends branches into the ambulacra. "This," 

 Mr. Carpenter says, " leads to the suspicion that each radial vessel of 

 an Echinus communicates directly with a corresponding vascular ring, 

 just as was described by Teuscher, and that the water-vascular and 

 blood-vascular systems are distinct, at any rate in the peristome and 

 ambulacra." And it is further pointed out that Koehler's results 

 would have had a still higher value if they had been more fully com- 

 pared with the results of other anatomists, who have, in Asterids, 

 Ophiurids, and Crinoids, already described independent blood- vascular 

 and water- vascular systems. 



* Quart. Journ. Micr. Sci., xxiii. (1883) pp. 597-616. 



