ECOLOGY AND TAXONOMY OF HttUmeda 21 



be the earliest comparatively detailed examination of internal structm-e 

 in Halimeda. More intensive microscopic examination was not under- 

 taken until over a century later, first by Askenasy (1888) and then by 

 Barton (1901). Ellis particularly noticed the pits and facets given to the 

 surface of Halimeda segments by the peripheral utricles, and compared 

 them with the surface patterns of cnidarian corals : 



We see in the greatest number of Corallines their surface full of holes ; 

 we saw the same in Escharas and Milleporas thirty years ago; since 

 that time magnifying glasses have been improved, so as to shew us, 

 that they are all orifices, for polype-like suckers; why should not we 

 now admit that glasses may be still more improved, so as even to make 

 us able to see what may be the intention and use of these minute 

 orifices, which according to all rules of reasoning, we must suppose to 

 approach in nature to them they are most alike. 



This provided part of the basis for considering Halimeda as an animal. 

 Ellis' conclusions had force because of his skill and reputation as a 

 microscopist. Linnaeus wrote to him, "I beg of you to lend me your 

 lynx-like eyes" (Library of the Linnean kSociety of London; Savage, 

 1948). Furthermore, ElHs worked with some of the best laboratory 

 hardware of the day including an "aquatic microscope" (Fig. 13) made 

 by a London optician and "improved" by Ellis specifically for examining 

 living corallines. I used Ellis' aquatic microscope at the Science Museum 

 (London) and found the resolution to be surprisingly good. Figure 14 

 shows a photomicrograph of the surface of Halimeda incrassata made 

 with it. The more obvious surface features of the plant can be conceived 

 almost as certainly as with a modern microscope. The smallness of the 

 field, and its curv^ature, are the main problems of these simple instru- 

 ments. Chromatic aberration led to some vexing difficulties, but not as 

 much as in the compound microscopes of the time. 



Ellis provided additional contemporary insights on microscopes and 

 viewing in a letter to Dr David Skene in 1770 (Library of the Linnean 

 Society of London; Savage, 1948). 



I find Wilsons or the Single microscope much the best ; there need not 

 be any piano convex glass screwd in at bottom if you have a good 

 illuminating concave speculum to throw up the light, and at the same 

 time to take instead of the piano convex on the bottom to screw on the 

 bottom a brass circular plate with a hole in the centre in proportion to 

 the size of your magnifier; the largest magnifier as No. 1 requires the 

 smallest hole, by this means in a clear day youll easily see the minutest 

 animal distinctly. Mr. Dollond has at my request fitted up a pocket 

 microscope that pleases most people ; it consists of my aquatic & Wilsons 

 combind together so as to be very little larger than the aquatic alone 

 2 



