CTENOPHORA. 723 



A single fibre is oval or circular in section, homogeneous, nucleated when develop- 

 ing. The superficial cells of the axis are ordinary ectoderm cells in Euplocamis 

 stationis, in others tactile cells, few in number, and adhesive cells which are replaced 

 in Euchlora (Owenia) rubra by cnidoblasts on the main axis, but not its branches. 

 An adhesive cell has a convex free surface studded with adhesive globules (p. 331), 

 and contains a muscle filament in connection with the fibres of the axis. The outer 

 part of the filament is spirally coiled to admit of extension when the cell is forcibly 

 elongated by the struggles of the prey. The branches of a tentacle, and the lateral 

 tentacles of Lobatae and Cestus, have the same structure as the main tentacle. 



The mesoglaea is firm in Cestidae and Beroidae, soft in others. It imbeds (i) 

 amoeboid nucleated ' connective tissue ' cells ; (2) fine irregularly branched nervous 

 filaments connected one to another, and to the muscle fibres 1 ; (3) muscle fibres, 

 composed of a sarcolemma, a clear cortex, a granular axial medulla with nuclei ; few 

 in number in the Cestidae alone ; disposed radially between the stomach, funnel, 

 ctenophoral vessels, and the surface of the body ; circularly round the stomach and 

 scantily round the body near its surface ; meridionally near the surface, between the 

 ctenophoral rows. The radial fibres are branched at each end, the others pointed. 

 Circular fibres surround the mouth in Cydippidae and Beroidae, and in all Cteno- 

 phora the sensory area. The latter can be deeply retracted into the mesoglaea : so 

 too the ciliated furrows or nerves, and to a greater or less degree the rows of cteno- 

 phoral plates, e. g. in Beroidae. 



The stomach is lined by ectoderm, similar to that of the body-surface; 'glance' 

 cells are sometimes wanting. Two stomachal ridges, covered chiefly by glandular 

 or granular cells, vis-a-vis to one another, are present except in Beroidae. A layer 

 of longitudinal sub-epithelial muscles, and a nervous plexus external to it, are found 

 in the stomach of that family, the musculature in other families as well. 



The endoderm of the funnel and the vessels is unilaminar : its cells flat, 

 polygonal, ciliated, except in the ampullae of the funnel vessels, at the sides of the 

 paragastric vessels, and the outer aspects of the ctenophoral, ivhere they are columnar, 

 vacuolate, non-ciliated (?), and disposed in a single or double ridge. The two forms 

 of cells pass one into the other. ' Ciliated rosettes,' or minute depressions into the 

 mesoglaea, lined by small ciliated cells, occur in the flat epithelium of the funnel 

 and vessels. Longitudinal and circular muscles are said to surround the vessels. 



The genital organs are invaginations from the ectoderm (Hertwig). In Beroidae 

 they form continuous bands of cells ; in Callianira, Hormiphora, Euplokamis close- 

 set masses of cells connected to the ectoderm by cellular cords. The cell-masses 

 grow into the endoderm. The testes have a sinus, except in Beroe, with an outer 

 wall of flattish cells, and an inner of nucleated protoplasm, from which the sperma- 

 tozoa are derived. The ovaries are solid, the cells of the outer wall vacuolate, of 

 the inner transformed into ova. 



The Ctenophora are classified by Chun as follows : 

 I. Tentaculata. Tentacles present. 



i. Cydippidae ( = Saccatae] : globular or cylindrical forms. Two long ten- 



1 They are possibly connected with the sub -ectoderm ic nervous plexus. The fine filaments 

 which underlie the ciliary furrows, Chun's nerves, are probably nervous. They extend below the 

 sensory area, where the different bundles anastomose. They are perhaps connected to the ciliated 

 ectoderm cells. 



3 A 2 



