On Defective Organization among the Araneidea. 1G5 



certainly quite distinct from real animal motion. In an inter- 

 esting memoir by Morren * on the genus Jphanizomenon, this 

 botanist ascribes to the agency of electricity motions some- 

 what similar to those of the Trichormus : Morren's paper is 

 ingenious and well worth perusal, but it must also be admitted 

 that his theory is based on insufficient grounds, and his analo- 

 gies rather far-fetched and fanciful. 



I have to notice also the occurrence in company with the 

 Alga just described of the Aphanizomenon incurvum of Mor- 

 ren, the only record of which as a British plant is that of Mr. 

 Thompson of Belfast, who discovered it in Ballydrain lake in 

 July 1838 (see ' Annals/ vol. v.). Shortly after this it was also 

 found in the pond of the Dublin Zoological Gardens by Miss 

 Ball, who possesses specimens from that locality in her col- 

 lection. 



In investigating the subject of the present paper I have 

 been enabled to examine dried specimens of Mr. Thompson's 

 Alga. For the opportunity thus afforded me of comparing 

 my plant with the authentic A. ? spiralis, I am indebted to 

 the kindness of Miss Ball, whose valuable collection that lady 

 obligingly allowed me to examine, and by whom I was libe- 

 rally supplied with any specimens I might require. 



XXVI. — Notice of several Cases of Defective and Redundant 

 Organization observed among the Araneidea. By John 

 Blackwall, Esq., F.L.S. 



Among the numerous difficulties with which arachnologists 

 have to contend in their endeavours to acquire a correct know- 

 ledge of the Araneidea, the great liability of those animals to 

 run into varieties, and the close resemblance which some spe- 

 cies bear to others, are not the least formidable ; indeed, as cir- 

 cumstances conducing largely to the introduction of fictitious 

 species on the one hand, and to the confounding of those which 

 are distinct on the other, they have proved fertile sources of 

 error and perplexity. Ample evidence of the accuracy of this 

 statement may be obtained by a careful comparison of the 

 writings of those naturalists who hold the highest rank as 

 authorities in this department of zoology. 



A considerable share of attention having been bestowed 

 upon variations in the colour and size of species, resulting 

 from differences in age, sex, food, climate, and other condi- 

 tions of a less obvious character, while those arising from ex- 



* Histoire d'un genre nouveau <le la tribu des Confervees nomme Aphani- 

 zomene; lu a l'Academie Royale de Bruxelles le 2 Decembre 1837. — See 

 Annals, vol. v. p. 82. 



