SCIENCE-GOSSIP. 



95 



grouped in a raceme which arises from the axil of 

 the uppermost leaf; they are thus below, but in 

 close proximity to the staminate catkins. In the 

 autumn of each year we may find on the same 

 branchlet pistillate catkins belonging to three 

 successive seasons. Thus, on a branchlet examined, 

 say, in September of the present year, iSg6, we 

 shall find, first, the dead woody remains of the 

 catkins originally formed in 1894, which reached 

 the flowering stage in 1S95, but which did not 

 mature and shed their seed until the winter of 

 1S95-6. Second, those formed in the autumn of 

 1895, now green and plump, but which will not 

 have matured their seed until late in the coming 

 autumn or winter. Third, those which, together 

 with the staminate catkins, are as yet in the 

 embryo stage, and are to attain the flowering 

 condition in the spring of 1897. 



As in the case of maple and sycamore, the 

 tendency to flower is first manifested by the small 

 lateral branchlets, but it eventually affects the 

 leading shoot also and, of course, prevents further 

 lengthening of the shoot in the original direction. 

 The diameter of the young yearly shoots of the 

 alder is moderate, being about three-sixteenths of 

 an inch. 



There is a peculiarity about the axillary buds of 

 the alder which is not, so far as I know, shared by 



any other British tree. Instead of being closely 

 seated in the axil of a leaf, as in most trees, the 

 bud is seated on a footstalk of one or more short 

 internodes, and thus, as Schleiden pointed out, 

 it has rather the character of a terminal than of 

 an axillary bud. 



In its main features the alder may be described 

 as a tree of small or moderate size, with an upright 

 trunk which preserves its distinctness nearly to 

 the top of the tree, and gives off, even from its 

 lower portion, strong diverging limbs, which in 

 their turn put forth secondary branches, all of 

 which, including the main limbs, terminate 

 eventually in bushy masses of stiff, ascending, 

 flowering sprays, but which have an irregular 

 appearance, and in consequence of their alternate, 

 instead of opposite, arrangement, and of the closer 

 angle they make with each other, exhibit a very 

 different appearance from the compact growth and 

 even outline of the sycamore. 



The leaves of the alder are somewhat small as to 

 size, and their stiff footstalks keep them apart 

 from each other, so that they do not overlap or 

 present a continuous surface to receive the light ; 

 thus, although much broken up, the general aspect 

 of the tree does not show any great variety of light 

 and shadow. 



(To be continued.) 



PULEX IRRITANS. 

 By John C. Webb, F.E.S. 



T N all probability the number of people who can 

 truthfully claim to be unacquainted with the 

 common flea is extremely limited. Most indivi- 

 duals know it only too well, especially those who 

 have the misfortune to travel on railways, and 

 these can testify as to its bloodthirsty nature, the 

 skilful manner in which it comes to the 

 attack, as well as the agility with which 

 it evades capture. Notwithstanding 

 all this, it is very rare to find anyone 

 outside the ranks of entomologists who 

 knows anything of the life-history of 

 the flea. Most persons that I have 

 met with are under the impression that 

 the fleas are born very small and 

 gradually grow larger, thus mistaking 

 the male, which is smaller than the 

 female, for the young insect, and the 

 female for the one which has reached maturity. 



It may not be uninteresting to some of the 

 readers of this journal, therefore, if I give a brief 

 description of the Hfe-history of this terrible 

 parasite, as verified by my own personal observa- 

 tions. The mature flea has already been so well 

 described by more eminent entomologists than 



%1- 



Fig. I, Egg of Flea. 



Fig. 2, Larva of Flta 



{PuUx iriitans). 



myself, that I cannot do better than repeat their 

 description. It is of a dark brown hue, and oval 

 shape, with small roundish head, having eyes on 

 either side, and furnished with formidable mouth 

 organs, consisting of the lancets, etc., which 

 it uses so effectively in wounding its victim, 

 and two four-jointed antennae. The 

 thorax is composed of three segments, 

 each consisting of an upper and lower 

 piece, and from the latter arise the six 

 legs which are so admirably formed 

 for leaping. The first joint of the leg 

 or coxa is rather thick, then follow the 

 trochanter, the fermin, the tiba, and 

 lastly the five-jointed tarsus which 

 terminates in two curved claws. The 

 abdomen consists of nine rings, the 

 last of which contains the pygidium, 

 so frequently used by the older microscopists as a 

 test object for a good half-inch objective, and 

 respecting which there has been much dispute in 

 days gone by. As already stated the male is con- 

 siderably smaller than the female, from which it 

 may readily be distinguished. 



After pairing has taken place, the female deposits 



