766 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and muscular layers there are bipolar and multipolar nerve-cells, whence 

 fine filaments extend in all directions ; this diffuse nervous system may be 

 compared with that found by the brothers Hertwig in the oral disc of the 

 Actiniae. The cells of the muscular layer often take part in forming the 

 ectodermal epithelium, and this shows that the muscular layer is not yet, 

 in this form, completely separated from the epithelium. Below the 

 muscular layer there are other nerve-elements which are connected with 

 the sub-epithelial nerves, and thus the nervous system forms a network 

 which extends through the whole ectoderm and embraces the muscular layer. 

 This nervous layer is specially connected with the phosphorescent property 

 of the animal. 



The septa, of which there are eight, consist of a supporting lamella, on 

 one side of which there are longitudinal muscles and on the other transverse 

 fibres ; there are also large luminous cells, and spindle-shaped nerve-cells 

 are to be found among the muscular fibres. 



The structure of the wall of the polyp is much more primitive ; the 

 ectoderm is alone muscular, but the transverse fibres contain no special 

 cells and belong completely to the epithelium ; below this are spindle- 

 shaped nerve-cells and luminous cells ; the supporting lamella contains a 

 well-developed plexus of connective-tissue cells; the endoderm has fat- 

 spheres and some unicellular glands. 



The sexless polyps have a special significance and structure ; there is 

 no true body- wall, the septa being attached to the oral disc ; the oesophagus 

 consists of filamentar cells with long and thick flagella, and between these 

 extraordinarily small elongated nematocysts are imbedded, the whole 

 forming a battery of nematocysts ; so that the sexless polyp may be called 

 a stinging polyp ; when the stinging organs are ejected the oesophagus is 

 cvaginated. 



Two of the septa of these sexless polyps are specially developed, their 

 free inner margin bearing a ridge made up of flagellate cells ; this ridge 

 extends from the septa to the walls of the spongy tissue of which the body 

 of the colony is composed ; by their action a constant movement of water 

 is kept up. It should be added that the oral disc of each polyp is provided 

 with nervous elements which bring about the evagination of the oesophagus, 

 and there are small light-cells. 



The large sexual polyps are all male, the ova being developed in the 

 rhachis, where they form four longitudinal cords, attached to the four sides 

 of the internal axial canal. As the eggs are placed near the asexual polyps 

 it may be supposed that all the polyps were primitively sexual ; some in time 

 became reduced, and the female elements passed into the interior of the 

 colony. 



Protozoa. 



Conjugation of Ciliate Infusoria.* — M. E. Maupas has studied the 

 conjugation of Onychodromus grandis and StylonicJiia pustulata. The former, 

 in conjugating, is always provided with two nucleoli ; in several individuals 

 the exchange of the male pronucleus was observed, and then its union and 

 fusion with the female pronucleus. Separation takes place a little later, 

 and by a kind of ecdysis the separated individuals renew all their appendages, 

 the mouth and buccal membranellse being alone wanting; the nucleus 

 grows and soon becomes a large clear spot which occupies the centre of the 

 body. Around the nucleus the cell becomes darkish and opaque ; this is 

 due to the presence of birefractive corpuscles of urate of soda, and of 



* Comptes Kendus, cv. (1887) pp. 175-7. 



