ARCHER AND DIXON, ON DESMIDIACEiE. 75 



able to find them or their nuclei in sections simply hardened 

 in chromic acid, but noticed occasional nuclei on the sheaths 

 of the fibres in the sciatic nerve. In most parts of the cord, 

 when simply hardened in chromic acid, it is certainly very 

 difficult to detect them; for, being about the size of the cut 

 ends of the smaller fibres and blood-vessels, they are scarcely 

 distinguishable in the confused and badly defined matrix in 

 which they are imbedded. Stilling, even with a magnifying 

 power of 1100 diameters, has failed to detect these bodies 

 in the cord of the Calf. But in preparations made according 

 to my method they may be seen with the greatest facility 

 under a power of 400 diameters, in consequence of the 

 superior definition. Even with the simple use of chromic 

 acid, however, they may be very readily found towards the 

 lower end of the cord, — in the coccygeal region ; for here 

 the white columns are very much subdivided by numerous 

 ramifying fissures containing pia mater and connective 

 tissue, in which the cells or their nuclei abound. 



Description of Two New Species of Staurastrum, by W. 

 Archer; a New Genus and Species of Desmidiace/E, 

 by the Rev. N. V. Dixon ; and some cases of Abnormal 

 Growth of Desmidiace^e, by W. Archer. 



(Read before the Dublin Natural History Society, on Friday, June 3d , 

 1859; extracted from the 'Natural History Review and Quarterly Journal 

 of Science,' for Oct. 1S59.) 



In these days of cancelling from our lists, and their con- 

 sobdation with others, of numerous species, or reputed species, 

 in the various walks of natural history, — and this, no doubt, 

 in many cases, with much reason, — it may appear unjustifiable 

 rashness and temerity on my part to come forward for the 

 purpose of describing the following two new forms to be added 

 to our lists of Desmidiacese. But in a more extended point of 

 view, in regard to what is a species and what is not, it seems 

 to me that naturalists are prone to err in one of two direc- 

 tions : they either restrict the number of species in their lists 

 within too narrow limits, or inordinately increase their 

 number by giving a name and specific rank to almost every 

 variation which they encounter. On the one hand, because, 

 between two hitherto recognised distinct, but allied species, 



