HARBWICKE'S SCIENCE-GOSSIP. 



273 



the third longitudinal vein in a curve or angle as 

 in the Tachinedre and Muscidse. 



The Anthomyiidce are separated from the various 

 groups of smaller or acalypterate Muscidse by the 

 alulets or scales being more or less highly developed. 

 (Ento. Mag. vol. 18, page 1.) 



The general characters of the genus Mydae as given 

 by the same authority, at page 27 of the same volume, 

 are as follow : viz. " Eyes bare, contiguous, or sub- 

 contiguous in male, arista plumose ; abdomen mostly 

 oval, and always unspotted ; alulets well developed, 

 the under scale being much longer than the upper 

 one : anal vein not prolonged to the margin of the 

 wing." 



The genus contains eleven species, which is sub- 

 divided into two groups, according as their legs are 

 wholly black or partly pale. 



My da urbani is a very common species, and may 

 be taken freely in the neighbourhood of offensive 

 matter, frequently near hedgerows during the summer 

 months. It is a rather robust creature, being inter- 

 mediate in size with the blow-fly and house-fly. The 

 thorax is marked with several dark bands ; the abdo- 

 men is of a greenish-brown shade ; the basal portions 

 ■of the wings and the alulets are ferruginous, and the 

 legs have a similar hue. 



The outline formed by the group of teeth found 

 in this creature bears a strong resemblance to the 

 shape of the group possessed by Musca vieridiana, the 

 basal portion being much longer than the generality 

 •of species exhibited, and is quite destructive in itself; 

 the similarity, however, is not continued to the 

 individual organs, these varying materially in form 

 at their free edges. 



The group is composed of ten primary teeth, and 

 three subsidiary rows of seven, six and three respec- 

 tively. No particular form can be assigned to the main 

 set as they are subject to variation, not only among 

 themselves, but also in different specimens. This 

 variation however is so constant, that it may be looked 

 upon as a leading feature in the dentition of this fly. 

 When taken in conjunction with the trident-shaped 

 terminations of the subsidiary rows, the laterals ter- 

 minate with the usual blow-fly type, and the whole 

 group is of a light clear amber colour indicative of 

 medium strength. 



Cardiff'. 



Gulls in Gardens.— Common gulls are very 

 beneficial. A friend of mine who keeps several tame 

 gulls allows them to run about in his kitchen- 

 garden among his cabbages, where they do much 

 good by eating the grubs. Ducks have been found of 

 much use in clearing away such pests as caterpillars, 

 but gulls have been found still more useful, because 

 their beaks are better adapted to hunt for the insects 

 among the folds of the leaves. They cause no injury 

 to the vegetables.— W. Harcmrt Bath, Birmingham. 



THE FOOD HABIT OF PETALOMONAS 

 CARINA TA. 



By Dr. Alfred C. Stokes. 



IN the June issue of the ' Annals and Magazine of 

 Natural History,' the writer described an in- 

 teresting fresh-water infusorian, under the name of 

 Ptfalomonas carinata, its most conspicuous character, 

 and the one suggesting the specific title being the 

 elevation of the dorsal aspect into a median longi- 

 tudinal more or less keel-like ridge, the two sides of 

 this roof-shaped surface sloping to the right-hand and 

 left-hand margins respectively, and having at times 

 a slight lateral concavity. The body itself is broadly 

 ovate or suborbicular in outline, the ventral surface is 

 somewhat concave, and the endoplasm, although 

 granular, is transparent. The oral aperture is remark- 

 ably capacious, and the single flagellum appears to 

 originate, I think it does in reality originate, within 

 this oral fossa, an appearance conspicuous in all the 

 species which I have seen. 



Minute collections of what I have diagnosed to be 



Fig. 172. — retalomonas carinata. 



partially digested food-particles are usually noticeable 

 within the sarcode, but until recently I had not 

 observed the infusorian in the act of taking food, and 

 I was of course ignorant of its favourite diet. The 

 mode of obtaining nourishment is so interesting, and 

 in some particulars so inexplicable, that I desire to 

 call attention to it, hoping that those accustomed to 

 work with comparatively high magnifying powers 

 ( T ' s and Vg objectives for instance), may meet with the 

 animalcule, and may be able to explain what to the 

 writer is rather obscure. 



When the petalomonas finds a spot richly supplied 

 with minute bacilli, it comes to rest. The flagellum 

 is then thrown around to one side of the body, the 

 base being apparently strained against the edge of 

 the oral aperture, the entire lash, with the exception 

 of the free extremity, being practically motionless ; 

 the distal end alone vibrates in quite regular, almost 

 rhythmical beats. The effect of these quick move- 

 ments is that the bacilli are dashed against the 

 motionless portion of the flagellum, down which they 

 involuntarily glide to the oral fossa. Here they fre- 

 quently regain their liberty, darting in and out of the 

 aperture or collecting around the margin like flies 

 around a honey-drop ; occasionally they dart away 

 and out of the field. Yet there is usually quite a 

 steady flow of bacilli in almost Indian file down the 

 basal part of the flagellum, or across the somewhat 



