INTRODUCTION. XVU 



the shell of a crab, or a limpet, from which the entire flesh 

 has been removed and replaced by a tenacious glaire. No 

 doubt the first part of the process consists largely of ma- 

 ceration, and continued pressure, by means of which the 

 juices of the food are extracted. 



The nutritive matters thus obtained are then subjected 

 to the action of the bile. No anatomist, I believe, has as 

 yet attributed a liver to these animals, but I have little 

 doubt that such is the character of a structure which I am 

 about to describe. In dianthus, crassicornis, Peachia undata, 

 and others, the stomach-wall is lined on the interior side of 

 its upper portion (the side, I mean, which is within the 

 interseptal chambers) with a thick highly- coloured sub- 

 stance. In the first two named this is yellow or orange, in 

 the last salmon-red. This lining is (dianthus) about half a 

 line in thickness, of a pulpy tissue, arranged in irregular 

 lobules, covered with a ciliated epithelium (Tlate XI. fig. 

 1, d). On being crushed down, the pulp is found to be 

 composed of a nearly uniform mass of yellow fat-cells, the 

 largest of which are about '0003 inch in diameter, and the 

 smallest immeasurable points. Cnidae occur numerously in 

 the true stomach-wall, but none in this lining-coat. I am 

 justified, then, in presuming this organ, from its colour, 

 form, position, and structure, to be a liver.* 



In Aiptasia I find what I think an analogous structure, 

 but with a slightly varied position. The septa, instead of 

 being inserted into the stomach-wall from the point where 

 they spring off to the summit, recede from it at their upper 

 part, where their edges carry rounded pulpy lobes, which 

 under pressure consist of a clear tenacious sarcode, carrying 

 a moderate number of brown pigment-cells. The sarcode 

 is composed of globose cells, averaging "0005 inch in 

 diameter, each containing more or fewer oil-globules, 



* As an example of the need of caution in such observations as these, 

 I may be pardoned for mentioning the following circumstance : — While 

 viewing the surface of the pulpy tissue above described under a good 

 reflected light with a power of 133 diameters, I saw it forming irregular 

 lobes, with deep narrow sinuous depressions. Over the surface, and 

 chiefly following the lines of the sinuosities, I noticed meandering white 

 lines, like very slender branching threads. The thought that I had dis- 

 covered veritable nerves immediately occurred to me ; but turning the 

 mirror of the microscope to test the observation with a different angle of 

 the light, I found I had been looking at merely the light reflected from the 

 edge of the smooth lobules I 



