On the Nervous Sijstem of Actinia. 69 



mnst acknowledge the excessive difficulties wliicli accompany the 

 attempt. The irritabihty-of the muscular tissues, their persistent 

 contraction during manipulation, the confusion caused by the 

 abundance of diflerent cellular histological elements, and the general 

 sliminess of the whole, render the minute examination very trouble- 

 some and usually very unsatisfactory. Keagents are useful for 

 rough examinations ; but when the most dehcate of the tissues are 

 to be examined they must be floated under sea-water, and this must 

 be the medium in which they must be examined under the 

 microscope. Carmine solution, osmic acid, and spirits of wine in 

 weak solutions are useful after the natural appearances have been 

 determined, but they exaggerate some histological elements and 

 destroy others. 



G-reat care must be taken in making the thin sections, and no 

 tearing must be allowed ; for it is of paramount importance, in 

 endeavouring to trace the nervous system, that the relative position 

 of parts should be retained. 



It is useless to rely on any observation made with object-glasses 

 lower than yVinch focus (immersive). 



In examining the chi'omatophores. Actinias with very bright- 

 coloured ones, and other specimens with these organs dull in tiut, 

 should be selected. Fresh subjects should be obtained, and it is not 

 necessary to kill them first of all. The blades of very dehcate 

 scissors should be allowed to touch the desired chromatophore close 

 to its base, and then as the Actinia commences to contract, they 

 should be brought together gently and without wrenchincr the 

 tissues. By this method the chromatophore will remain on the 

 blades. Two or three chromatophores may be removed, with their 

 intermediate tissues, without injury to the animal ; but. of course, 

 the excision must not be too deep, or the endothehimi will be cut 

 into. 



A dropping tube should be used to wash the chromatophore off 

 the blades on to a glass shde, where a drop of sea-water awaits it. 



Sections are by no means easy to make, but they are best 

 performed under a power of 10 diameters with fine scalpels. The 

 forceps must not be employed, as it crushes the tissues. If possible, 

 very shght pressure should be exercised on the thin glass, which is 

 to be placed very carefully and wet over the object. After the 

 examination, carmine should be added, or osmic-acid solution, 1 per 

 cent, in strength ; but no results can be rehed on which are derived 

 from the examination under the influence of reagents alone, as they 

 modify the natural appearance greatly. 



So fer as the chromatophores are concemal, my iuvesticyations 

 took the following course : — 1. Eotteken's researches on the alco- 

 holized ^c/^'n/a were followal in recent specimens. 2. The tissues 

 of the chromatophores, of their margins, and of the spaces between 



