ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 69 



doubt tliat the gelatinous material of the medusa-disc cons'sts of a net- 

 work of organized substance, in the meshes of which sea- water is retained 

 by adhesion ; the fibres which traverse it are either smooth or granular. 

 Of the cells, the most common are rounded bodies which, with Hamann, 

 the author calls colloblasts, as they appear to form the mesogloea which 

 they excrete in concentric layers on their surface. As Glaus and 

 Hertwig have shown, these cells arise from the endoderm of the upper 

 surface of the stomach, whence they wander into the mesogloea ; they 

 increase by division, and appear to take in nourishment which is diffused 

 through the substance of the jelly. Of other cells there are bi-, tri-, or 

 multipolar bodies which are distributed more irregularly than the collo- 

 blasts, and they all appear to be in connection with one another. There 

 are also amoeboid wandering cells, and quite irregular cells, which the 

 author is inclined to regard as being poison-glands ; the latter have only 

 been observed in Phyllorhiza punctata. 



In the marginal sensory organs we may distinguish the marginal 

 body itself; the ephyral lobe on either side of this body; the covering 

 plate ; the pads on the surface of the lobes which is turned towards the 

 marginal body ; the projecting end of the radial canal below the marginal 

 body ; the sensory pit behind and above the body, and the gelatinous 

 vpall which separates the sensory pit from the pouch of the marginal 

 body. All these are dealt with by the author in considerable detail. 



The subumbrella carries the reproductive organs; the female, and 

 generally also the male organs are found in the mouth-arms ; the 

 greater part of the subumbrella is occupied by the muscle of the disc, 

 which, by its rhythmical contractions, effects the locomotion of the 

 Medusa. Smooth and transversely striped muscle-cells may be dis- 

 tinguished, the latter being best and most numerously developed. The 

 marginal bodies and their surroundings form a complex of sensory 

 organs, which perceive the waves of sound and light, and such changes 

 as take place in the chemical quality of the water. The stimuli are 

 conveyed to the ganglion-cells, which lie behind the marginal body and 

 in front of the seusory pit. From this central organ locomotor stimuli 

 start, which pass to the nerves which lie in the subepithelium. These 

 extend centripetally along the radial canals, and from the radial nerve 

 numerous circular nerves are given off which follow the margins of the 

 primary folds of the muscle-plate, and innervate the ganglionic cells 

 which lie above the true muscle-plate. Thence other fine nerves pass 

 off which spread out in the muscle-plate and are directly connected with 

 the muscle-corpuscles. The nerves anastomose frequently, and so form 

 a plexus which invests the whole of the lower side of the disc. The 

 muscle has a flexor function, while the hard and very elastic supports of 

 the muscles have an antagonizing action, and serve as extensors. 



The gastro-vascular system and the mouth-arms are next described. 

 There can be no doubt that, in the Ehizostomata, digestion is principally 

 effected in the distal parts of the whole gastro-vascuiar apparatus ; 

 thence the prepared food passes by the arm-canals into the central 

 stomach, whence it makes its way by the vessels of the disc into the 

 important organs on the edge of the disc and in the subumbrella. The 

 author considers that the vascular system of the disc is chiefly an 

 apparatus for transport and assimilation, which is, perhaps, comparable 

 to the blood-vdscular system of the Ccelomata, from a physiological 

 point of view. There are, apparently, no special renal cells, and the 



