SCIENCE- G OS SI P. 



-described have been figured as distinct species, such 

 •as possibly M. rliomboides. and it is not unlikely 

 that some may consider M. l&padella as a variety 

 of M. solidus. 



I think all the members of the family are vege- 

 table feeders, and may be seen grubbing with the 

 "pick" among Confervae and decaying water- 

 weed. The mastax is also extruded on the ven- 

 tral surface — there is a bend of the carapace 

 for this purpose— and may sometimes be watched 

 nibbling at the surface of a weed. The cilia 

 as usual are used to create currents, bringing 

 streams of sediment into the mouth, and in 

 ■swimming. 



I kept the water by me, examining it from time 

 to time, always finding fully grown individuals 

 (figs. 9 and 10) ; but with these were other forms, 

 smaller and of different outline. As time went 

 on some Philodina made their appearance, the 

 Metopidia decreased in size, then in number, until 

 on the 7th of April, from a dip that would a month 

 previously have produced hundreds, I could only 

 find one, which is of the shape shown in figs. 7 and 

 S ; also five or six Rotifer vulgaris, two or three 

 Philodina citrina, and several Monostyla lunaris. I 

 also found Callidina parasitica, which I was puzzled 

 to account for till I observed an Assellus creeping 

 among the decaying weed at the bottom of the 

 jar on April 20th. The Callidina had left the body 

 of the host, and in their independent state were 

 certainly thriving and many in number. 



At first I was inclined to regard the various 

 forms of Metopidia as different species, but watch- 

 ing the appearance of a young one from the egg 

 (figs. 1 and 2), I was puzzled by its great difference 

 in outline from the parent species, and by the 

 presence of short spines at the base of the cara- 

 pace, which I regarded as a specific characteristic. 

 This young one was ^ of an inch in length. It 

 took nearly three-quarters of an hour to wriggle 

 free of the shell. The carapace was not well 

 marked, the body was granular and semi-opaque, 

 and it was decidedly cylindrical in shape. The 

 form that seemed most nearly allied to this is that 

 figured as 3 and 4, which appears not unlike the 

 M. rhomboides of Hudson and Gosse. Its length 

 was 2^ of an inch. The lateral view shows that 

 the body has not properly developed into the lorica, 

 but still retains much of the shape that characterised 

 the young one when it issued from the egg. There 

 are no signs of the spines at the base of the cara- 

 pace, they apparently having been absorbed. More 

 plentiful than this form was the oblong one figured 

 as 5 and 6. The length of this was s i_ of an inch, 

 but it was exceedingly thin, and consequently very 

 difficult to keep still in a live-box. This possibly 

 may be Squamella oblonga. 



It was at this stage that the chief difficulty of 

 my investigation commenced. In this, which I 

 conjecture to be the third form, there are no spines 

 at the base of the carapace : they reappear more 



marked than ever in the fourth, again disappearing 

 in the full-grown rotifer. 



The fourth stage is figured as 7 and 8. and has 

 been familiar to me for j'ears. Its length is still 

 r^g of an inch, but it is distinctly more solid. In 

 every detail, with the exception of the base of the 

 carapace, it agrees with the final form (figs. 9 and 

 10), which has reached a length of ^ of an inch, 

 and is, I understand, to be found still larger. The 

 male made his appearance, after some time, on 

 February 17th (figs. 11 and 12). He was t^, of an 

 inch in length, and, like all male rotifers, very 

 restless and active. 



The ordinary egg is quite plain (fig. 13), but 

 after the males had been seen, the "resting egg," 

 or so-called " winter egg," was found covered with 

 minute spines and about ^ of an inch in length. 



I am led to think that these are all stages in the 

 growth of the same species, for the following 

 reasons : (1) At one time there were no rotifers 

 present except the fully grown form ; (2) the very 

 fairly good though accidental isolation not com- 

 plete, as the appearance of other genera proves ; 

 (3) the known variety of form in the young of this 

 genus ; (4) all details, pick, eyes, mastax, place of 

 dorsal and lateral antennae agree ; (5) only in the 

 largest size were eggs to be seen ; (6) the egg, 

 5 ig of an inch in length, is obviously too large for a 

 rotifer -yJ- 5 of an inch in length, from end of toe to 

 point of hood. Otherwise I should have been in- 

 clined to think that fig. 1 was the early form of 

 fig. 7, and that the egg of figs. 3, 5, 9 had not 

 been found. 



90 Belsize Road. London, N. W. 



MOSQUITOES AND MALAKIA. 



By E. Beunetti. 



rFlHE insects popularly known as gnats and 

 -*- mosquitoes, included in the Dipterous family 

 Culicidae, have been receiving especial attention 

 during the past few years, owing to the discovery 

 that several of the species have the ability to 

 transmit malaria to human beings. 



There are probably about 300 described species 

 from all parts of the world, but a considerable 

 number of them will doubtless prove to be mere 

 varieties. As an example it may be noted that 

 between thirty and forty " species " of the genus 

 Culex have been described from North America, 

 whereas the number of true species is reduced to 

 fourteen only by our latest authority, Mr. L. O. 

 Howard, in his admirable paper published last 

 year on the " Mosquitoes of the United States." 

 Six (jut of Walker's eleven North American species 

 of Culex — mostly from Hudson's Baj* — are now 

 reduced to synonymic rank. 



The European species of this family have been 

 excellently revised by Ficalbi, who introduces at 



