HARD WICKE ' S S CIE NCE - G O SSI P. 



197 



cannot identify the two last species, with Pritchard's 

 C. bicuspidatus and C. eaudatus, as neither of them 

 agree in all their characters with either of those 

 species. 



Those of your readers who are fortunate enough to 

 possess the parts already published of Dr. Hudson's 

 work on the " Rotifera" will perceive that the pre- 

 dictions in reference to the recasting of the genera 

 in the family Euchlanidota have been more than 

 verified. In his classification of the rotifera he has 

 first divided them into four natural orders, according 

 to their mode of locomotion and the structure of the 

 foot. The first of these ideas appears in Dujardin's 

 classification, and the second in Leydig's. To these 

 orders he has given the following names : — 



Fig. 120. — Colorus dejlcxits. 



Fig. 121. — Colurus sp. 



Fig. 122. — Colurus sj>. 



Rhizota (the rooted), which are fixed when adult. 

 Ex. — Floscularia, Melicerta, etc. 



BDELLOIDA (leech-like), that swim with their ciliary 

 wreath, and creep like a leech, etc. Ex. — Rotifer, 

 Philodina. 



Ploima (the sea-worthy), that only swim with 

 their ciliary wreath. Ex. — Notommata, Colurus, 

 Brachionus, etc. 



Scirtopoda (the skippers), that swim with their 

 ciliary wreath, and skip with arthropodous limbs. 

 Ex. — Pedalion. 



He shows that the animals contained in these orders, 

 with a few exceptions, differ from each other first, in 

 their habits and, secondly, in the structure of the foot, 

 in the arrangement of the ciliary wreath, and in the 

 form of the trophi (jaws). The rotifers we have been 

 considering belong, of course, to the sea-worthy order 



(Ploima), an order containing no less than fourteen out 

 of the nineteen families into which Dr. Hudson has 

 divided the Rotifera. The genus Colurus is placed in 

 the sub-order Loricata (in which the corona and ciliary 

 wreath is various in shape, but never rhizotic, and 

 bdelloidic only in the Pterodinadse ; the trophi [jaws] 

 are of different types, but never bdelloidic, and 

 rhizotic only in the Pterodinadse), and in the first 

 division of that order, in which the animal's foot is 

 jointed, sty late or furcate, not transversely wrinkled 

 nor wholly retractile. This division comprises the 

 following families : Rattulidse, Dinocharidre, Sal- 

 pinadae, Euchlanidse, Lepadelladse, and Coluridse, 

 the characters of the latter being given as follows : 

 lorica compressed, open beneath ; head distinct, 

 surmounted by a retractile, arched chitinous plate. 

 This arrangement appears a very convenient one, and 

 will, I believe, commend itself to students of the 

 Rotifera ; but for a complete account of his different 

 genera we shall have to wait for the subsequent parts 

 of Dr. Hudson's great work. So far as this locality 

 was concerned last summer was a complete failure in 

 regard not only to this class of animals, but also in 

 respect of the microscopic fauna generally. I trust, 

 however, that the coming summer may make amends, 

 and if this should be the case I intend thoroughly to- 

 work the few "ponds and ditches "of this locality, 

 feeling assured from the experience of the past, both; 

 my own and that of other microscopists, that this is 

 the only certain method whereby one may hope to 

 compile an accurate and complete list of species. 



J. E. Lord. 

 Rawtenstall. 



GOSSIP ON CURRENT TOPICS. 

 By W. Mattieu Williams, F.R.A.S., F.C.S.- 



WHAT shall we do when our coal is exhausted ? 

 Among the replies to this very practical 

 question, that which is discussed by Mr. Starkie 

 Gardner in a paper on the utilization of the internal 

 heat of the earth is interesting and promising. A 

 step in this direction has already been taken at Perth, 

 in Hungary, where a well has been sunk to the depth 

 of more than 3000 feet, from which water is already 

 raised at a temperature of 16 1° Fahr., and the boring 

 is to proceed until 178 is attained. At this tempera- 

 ture all the ordinary cookery operations of stewing 

 and so-called "boiling" may be performed, most of 

 them very much better than at 212 . 



The extent to which this source of heat is practically 

 available depends, of course, upon the average thick- 

 ness of the earth's solid crust, or the depth at which 

 the required temperature is reached. Mr. Gardner 

 maintains that the movements of the crust of the earth 

 correspond more nearly to a thickness of ten miles 

 than of fifty, and I quite agree with him. There are 



