: 54 



HARDWICKE'S SCIENCE-GOSSIP. 



and half that number the opposite end. These minute 

 orifices measured the ^ by the j^ of an inch. 



When first deposited, the eggs appeared to have 

 already assumed the mulberry condition, the yolk 

 being aggregated into spirules — ranging in diameter 

 from the ^ m to the 5i ^ 5 of an inch. The ova are so 

 nearly diaphanous, that the process of incubation and 

 development of the embryo, can, with an instrument 

 armed with adequate power, be viewed throughout ; 

 when steadily watched the marvellous changes and 

 differentiation of parts are wonderful in the extreme ; 

 and perhaps there are few objects of greater beauty 

 and interest for the microscopist than that afforded 

 by pulex in its nascent stage. (See Figs, magnified 

 50 diameters, Nos. 169 to 174.) In thirty-six hours the 

 blastoderm is seen to occupy about one-third of the 

 ovum's length (see Fig. 170) and next day the crene- 

 lated embryo has extended itself along one side of 

 the eerr, curving: round the ends so as to surround 

 three-fourths of the yolk ; on the third day, the seg- 

 ments of the larva are distinctly differentiated, and 

 may be counted ; the yolk is now about one-half 

 absorbed. The larva is coiled round, and almost 

 fills the ovum on the fourth day of incubation, the 

 head and thirteenth segment being nearly in contact, 

 next day or sometimes on the sixth day it hatches 

 out, and at once begins a very active and energetic 

 existence. 



The larva resembling elongated little worms are 

 like other dipterous maggots, destitute of feet, they 

 move continually with a lively serpentine action, 

 occasionally rolling themselves into a spiral ; on the 

 anterior part of the head and in front of the 

 mandibles, are four tubercles, each digitated on the 

 apex with five spinous hairs in a straight line, with 

 these they pull themselves forward ; little tufts of 

 hair also appear on each of the segments, probably 

 protecting the spiracles, while the thirteenth segment 

 bears hooks ; all the processes apparently assist in 

 locomotion ; when placed upon the back of the hand 

 a slight prickly roughness is felt, as the larvae sway 

 about with eager restlessness, doubtless in search of 

 food ; there are two small antennae, but no perceptible 

 eyes ; there is also a spine tipped tubercle, on the 

 back of the head, the oval base of which appears 

 through the diaphanous structure. 



All attempts to feed the larvae were unsuccessful — 

 flies living and dead were offered them, but remained 

 unnoticed— they rejected whatever was placed beside 

 them for food, and usually died in a few days ; hence 

 a chrysalis was a rarity, and one or two could only be 

 occasionally obtained from a dozen maggots ; when 

 this occurred the pupae were the only survivors, the 

 other larvae (having gradually disappeared without any 

 means of escape) had probably been devoured. 

 When favourably located they evidently find food in 

 abundance, and where animals are infested with fleas 

 the larvae may possibly subsist upon the skin ex- 

 cretions, and thus to some extent act as scavengers. 



In Mr. Harkus's experiments, the rarity of cocoons 

 was owing to inability to feed the maggots. No doubt 

 if suitable food had been given, the greater number 

 might have matured, and numerous repetitions of the 

 attempt would have been spared ; in spite of many 

 failures the undertaking was persistently carried 

 through ; and the progress of the embryo sketched 

 from its earliest stage onward. Any exposure of the 

 larva? to cold or damp was immediately fatal. This 

 should be a useful hint to those who possess a 

 superfluity of fleas, as by reducing the temperature of 

 rooms so infested their numbers would be considerably 

 lessened. The larvae, as the pupa stage is approached, 

 assume a red hue, and about eight days from hatching 

 spin a cocoon like a fluffy speck of white cotton ; 

 the threads composing it are closely woven, and of 

 extreme tenuity ; when attached to a textile material 

 similar in colour, these must be very difficult of 

 detection. A cocoon from which the flea has issued is 

 shown in Fig. 177. A cocoon was opened after the 

 inmate had divested itself of the pupa case, but still 

 remained enveloped in a filmy transparent integument ; 

 this pellicle covered the insect completely, following 

 each leg and the antennae continuously. The immature 

 flea is shown as seen through this gauzy mantle in 

 Fig. 178. This together with the chrysalis case, is left 

 in the cocoon on emergence, which occurs in about 

 nine days. 



The translucency of the embryo flea, before be- 

 coming a pupa, so completely enables the internal 

 structure and action of the various organs to be 

 visible, that in point of actual interest there can be no 

 comparison between the living entity and an object 

 ;t Dead and buried and embalmed." Moreover, in 

 closely and steadily 'watching and sketching the 

 development step by step of any creature, the 

 microscope is applied to its legitimate use — as a tool 

 in the hands of the naturalist or enquirer. It will be 

 seen that about four weeks is required to metamorphose 

 the speck of vitalised matter contained in the minute 

 ovum of Pulex irritans into a suctorial tormentor, 

 which for its powers of annoyance, can neither be 

 despised nor ignored. 



M. II. Robson. 



Raised Beach at Sark. — While visiting the 

 Channel Islands last month, I went over from 

 Guernsey to Sark. A geological friend with me 

 pointed out what evidently appeared to be a raised 

 beach. It is about 100 yards up the road, after going 

 through the tunnel in the rock which leads from the 

 landing-place on the east side of the island. We 

 estimated the height of the raised beach at about 100 

 feet above the present sea level. Have any readers 

 of Science-Gossip noticed this raised beach, or 

 is it one well-known ? I picked out shells from it 

 looking exactly like some I had found on the well- 

 known shell beach on Herm. — Joseph Clark. . 



