405 



SCIENTIFIC REVIEWS. 



1. Ueher die Poly pen im Allgemeinen und die Actinien insbeson- 

 dere. On the Polypi in general, and the Actiniae in particular. 

 By WiLHELM Rapp, &c. With Three Coloured Plates. Wei- 

 mar, 1829. 4to. 



2. System der Acalephen, S^c. System of the Acalepha, being a 

 detailed description of all the radiated animals of the Medusa 

 Tribes. By Dr. Frederick Eschscholtz, &c. With Sixteen 

 Copperplates. 4to. Berlin, 1829. 



The vast tribes of animated beings which occupy the lowest 

 place in the scale of organization, present to the observing natura- 

 list an almost inexhaustible field for his researches. Notwithstand- 

 ing the valuable accessions to our knowledge in this department of 

 zoology, which have been furnished by the labours of Ellis, Cavo- 

 lini, Savigny, Lamouroux, and numerous others, both of our own 

 and other countries, it must nevertheless be admitted that number- 

 less blanks still remain to be tilled up by the diligence of future 

 inquirers. And, indeed, when it is considered that the creatures 

 to be studied are for the most part of excessive minuteness, and 

 inhabit an element different from our own, some of them being fix- 

 ed at almost unfathomable depths in the ocean, whence they are 

 brought within our reach only by some rare and fortunate chance, it 

 will not be wondered at that a multitude of circumstances respect- 

 ing their structure and mode of life should still be involved in ob- 

 scurity. To dispel at least a portion of this darkness, and afford 

 an additional contribution towards perfecting this branch of the 

 science, is the object of the works of which we now propose giving 

 ^ome account, 

 r The essay of Professor Rapp consists of an attempt towards a 

 natural arrangement of the polypi, under which head he means to 

 include not only those animals to which naturalists in general apply 

 the term polypi, viz. the naked and solitary polypi, and those 

 grouped together on a common stock, but also the Aciinice, which 

 animals he considers to be so nearly allied to the former, both in 

 structure and mode of life, that they cannot well be separated in a 

 natural classification. As the horny or calcareous stems with which 

 the greater number of polypi are connected, present far fewer dif- 

 ficulties in the way of investigation than the animals themselves, 

 or at least the parts which in a more eminent degree are possessed 

 of animal properties, it was natural for zoologists, in their systema- 

 tic arrangements of the dififerent species, to direct their chief atten- 

 tion to the various conditions of the stem, while they attached only 

 a secondary importance to characters which might be derived from 

 the animals. This circumstance has served to hinder the advance- 

 ment of this part of zoology in several Ways j and in particular it 



