172 SOME OBSERVATIONS ON THE 



suppose, of showing that "the comparison" was invidious, 

 enters into a statement of the periods occupied by Kirby and 

 Gyllenhal, in preparing their respective works. It seems our 

 celebrated countryman " devoted two or three years of his 

 undivided attention to the small group of 212 insects," and with 

 a result so imperfect, that out of the 100 species of Andrena 

 and Nomada, described by him, "one of the best hymenop- 

 terologists of the present time cannot ascertain above fifty 

 species, — i. e. exactly one half. Now if such be the extreme 

 difficulty of conveying, in definite and intelligible terms, the 

 characters by which species may be distinguished, inter se, 

 that two or three years of undivided attention to a small group 

 of 2\2 insects, by even a Kirby, has failed; what prospect 

 does Mr. Stephens offer to his subscribers, when he pledges 

 himself to describe, during the next twenty months, the 4,800 

 species recorded in his Catalogue, and not yet given in the 

 Illustrations; (when, too, he states explicitly in "the Post- 

 script," he can only employ a few hours stolen from relaxation 

 and repose each evening after the fatigues of the day,) to say 

 nothing of the hosts of minute Hymenoptera not indicated 

 even in the Catalogue, and the probable extensive additions that 

 will be made to our Fauna Insectorum in the course of the 

 current period ! ! ! I think I do not overrate the number of 

 British insects already known to exist, and still undescribed in 

 the Illustrations, at 6,000, which will give 300 a month for the 

 exercise of Mr. Stephens's descriptive powers ! ! ! ! If Kirby's 

 Mon. Apum Angliae, after all his care, tact, and time, and 

 with its limited extent of subject, still leaves the entomologist 

 unable to ascertain above 50 out of 100 Andrena and Nomada, 

 I am afraid Mr. Stephens affords just ground for apprehen- 

 sion, that to describe 300 insects per month is a task more 

 easily undertaken than well accomplished. However, " Nous 



Art. XVII. — Some Observations on the Structure and 

 Functions of Tubular and Cellular Polypi, and of Asci- 

 dice. By Joseph Jackson Lister, Esq. F.R. S. (From 

 the Philosophical Transactions, Part II. for 1834.) 



The science of Natural History is now advancing with a 

 rapidity which, twenty years ago, her most enthusiastic 



