966 RECORD OF CURRENT RESEARCHES RELATING TO 



Hydroida and Anthozoa on tlie one hand, and the Ctenopliora on 

 the other, are to be regarded as having been developed along two 

 different lines, having their point of union in a common ancestor. 

 In the Actinife and Hydroida the nerves and muscular fibres are 

 developed in the epithelium. Some epithelial cells give off muscular 

 fibres at their basal ends, while others form processes and become con- 

 verted into sensory cells or epithelio-ganglionic cells. When most 

 comjiletely developed, these pass from the surface of the body and go 

 to form subepithelial muscular cells or ganglia. Wherever nervous 

 elements are found in the mesoderm, they are only migrated organs. 

 In the Ctenophora the corresponding mesodermal parts do not arise as 

 such in the ectoderm, but they there only form indifferent amoeboid 

 cells, and they undergo their further differentiation after that they 

 have changed their position. In connection with this important differ- 

 ence there is yet another, which is to be found in the histological 

 characters of the mesodermal muscular fibres. In the ActiniaB and the 

 MedusEe there are bundles of muscular fibres grouped around a proto- 

 plasmic multinucleated axis ; in the Ctenophora the muscular fibres 

 are all of them elongated multinuclear cells, which have arisen from 

 the growth of a single uni-nucleated cell, and which are invested by 

 a covering, which is not made up of sej)arate fibrils. 



Led by these facts, the author has come to the conclusion that the 

 Ctenophora have arisen from very "indifferent" primitive forms, in 

 which the only indication of the characteristics of the Coelenterate 

 phylum was probably the tendency to a radially symmetrical arrange- 

 ment of the organs. Even the prehensile cells are so different that it 

 is hard to imagine that they had the same origin as the parts which 

 are regarded by Professor Haeckel as being homologous with them in 

 the other Coelenterata (" stinging-cells ') ; and Hertwig holds that the 

 Ctenophora are but very distant allies of the rest of the Coelenterata. 



Preparation. — Osmic acid was used as a hardening material, carmine 

 as a colouring. For maceration purposes a soluti'-"- ,f • 05 jier cent, 

 osmic acid, containing -2 per cent, acetic acid, was used. No good 

 results were gained by the use of chromic acid, bichromate of potas- 

 sium, or gold chloride. Observations in the fresh state are of great 

 importance. 



General View. — Along the body of a Ctenophore three axes may be 

 drawn. The longitudinal or primary passes from the oral to the aboral 

 pole, and this is generally the longest ; the transverse axis can best be 

 made out in the tentaculate forms ; the sagittal axis is perpendicular to 

 the other two. No true right or left, dorsal or ventral surfaces are to be 

 made out, but only an oral and an aboral end. The greater part of the 

 body is gelatinous, and this portion is extraordinarily rich in water. 

 The sensory body or " ganglion " and the polar areas are placed on the 

 aboral side of the body, and the former exactly occupies the centre of 

 the end of the primary axis. From the sensory body there arise eight 

 ciliated grooves, which are continuous with the eight rows of cteno- 

 l^horal plates; these form meridional bands. The most important 

 parts of the gastrovascular system are the stomach and the funnel ; the 

 latter leads into the peripheral canal system, which consists of three 



