INFUSORIAL ANIMALCULES. 



151 



Bid our space permit, many other arguments might be adduced in 

 favour of the views we have herein advocated ; but we must refer the 

 reader to the works of Kiitzing and Ehrenberg for further informa- 

 tion. 



Dr. Gregory believes that a large number of those Diatomacese 

 usually given as separate species, are nothing more than transition 

 forms of the same ; and that more extended observation has proved 

 that form, shape, or outline is not nearly so permanent a character as 

 had been imagined ; and he adds, " the more the Diatomacese are 

 studied, the more we perceive that, in many species at least, the shape 

 or outline is subject to endless variations."* 



The markings of the Diatomaceae are best seen when mounted dry : 

 they are usually mounted in Canadian balsam, or weak spirit and 

 water. Before quitting these interesting objects, we shall notice a few 

 of the commoner forms, reserving our remarks upon other species 

 until we come to fossil Infusoria. 



Naviculce. Navicula is the Latin word for ship, and has been ap- 

 plied to these little creatures from 

 their resemblance in form to a 

 long ship or boat. In the cata- 

 logue of the microscopist there are 

 upwards of twenty-four different 

 species named, fourteen of which 

 are at the present day found alive, 

 fig. 98, Nos. 1, 2, and 3. From 

 their beauty and minuteness, they 

 are used as test objects. It was 

 only in 1841 that Mr. Harrison, of 

 Hull, discovered the beautiful longi- 

 tudinal and transverse sir ice (groov- 

 ings) on the Navicula hippocampus, 

 or sea-horse ship, No. 1. A curved 

 graceful line runs down the shell, 

 in the centre of which is an ex- 

 panded oval opening, and smaller 

 ones at each end. Near to the fi 



central opening the dots elongate L Navicu i a hippocampus. 2. NavULla an- 

 crossways, presenting the appear- gulata, magnified 250 diameters. 3. Navi- 

 ance of small short bands. The cula Spencerii, magnified 350 diameters. 



* Dr. Gregory, " On a remarkable group of Diatomaceous Forms/' Quarterly 

 Journal of Microscopical Science. 



