ZOOLOGY AND EOT AN Y, MICROSCOPY, ETC. 741 



EcMnodermata. 



Nervous System of EcMnodermata.* — Dr. C. F. Jickeli deals, m. 

 Lis second preliminary comnirmication, with the nervous system of 

 Asterids. He is able to confirm the chief results of preceding inquirers. 

 The ambulacral nervous system, in the region of the mouth, exhibits a 

 distinction of the parts of the masses of nerve-fibres ; the ventral longi- 

 tudinal fibrous masses of the radial ambulacral nerves pass into the 

 circular fibres of the oral ring. If a transverse section be made through 

 an ambulacrum of Asterias rubcns close to the mouth, fibres are found in 

 the dorsal part which run parallel to the direction of the section, while 

 ventrally there is a rounded body made up of fibrils which have been cut 

 across. In Stichaster rosem, a separation of a ventral from a dorsal 

 mass may be made out throughout the whole length of the ambulacral 

 nerve. 



The subepithelial plexas is much more highly differentiated than has 

 been hitherto supposed. Lange's nerve is seen in cross sections to be a 

 paired thickening of the ventral wall of the perihasmal canal. Careful 

 histological investigation shows that it is made up of a delicate flattened 

 epithelium which invests the whole of the perihsemal cavity, of large 

 ganglionic cells lying directly beneath this, and having their processes 

 woven into a fibrous layer, in which separate ganglionic cells are 

 imbedded, and of a lamella of connective tissue which forms a parti- 

 tion between the ambulacral nerves and those of Lange. The latter 

 accompany the ambulacral nerves along the groove, and take part in the 

 formation of the oral ring. Between two successive ambulacral plates 

 the nerve extends, with a continuation of the perihaemal canal, as far as 

 the adambulacral plate, where it forms a swelling ; from this a cord may 

 be traced into the fibrous mass of the muscle between the ambulacral 

 and adambulacral plate ; in some cases, e. g. Luidia Sajsi, it may be 

 traced on to the neighbouring parts of the body-wall. 



Dr. Jickeli announces the discovery of a fourth system of nerves, 

 which forms a layer of fine fibrils intermixed with stellate cells at the 

 base of the epithelium of the digestive tract. This was best seen near 

 the anus of Astropeden andromeda. 



Ccelenterata. 



System of Siphonophora."|" — Prof. E. Haeckel proposes a new theory 

 to explain the organization of the Siphonophora. This he calls th& 

 medusome theory. 



(1) The primary larva which first arises from the gastrula of the 

 Siphonophora is always a simple medusa-person. It may be more or 

 less modified cenogenetically, but it has always great palingenetic 

 significance. 



(2) This primary larva apjiears in two essentially different forms 

 which may be called the Disconula and the Siphonula ; according to the 

 presence of one or the other we have the two subclasses of Disconanthfe 

 and Siphonanthse. 



(3) The Disconanthae, which contain the single order of Chondro- 

 phoridte or Porpitari^e, are developed from the regular and octoradial 



* Zool. Anzeig., xi. (1888) pp. 339-42. 

 t Jeuaische Zeitschr. f. Naturwiss., xxii. (1888) pp. 1-46. 

 1888. 3 E 



