SCIENCE-GOSSIP. 



257 



DEVELOPMENT OF THE ALDERFLY. 



By W. H. Nunnev. 



TTAVING in the summer of 1888 collected a 

 large number of the eggs of the common 

 so-called "stone-fly" (Sialis lutaria), I placed the 

 reeds upon which they were in water, in order, if 

 possible, to watch the transformations. The result 

 exceeded my highest expectations, for in about a 

 week from the date of capture I possessed 

 hundreds of the 

 young larvae of 

 different ages. 

 The later-earlier 

 stages, if I may 

 so term them, of 

 these larvae have 

 been fairly well 

 described by the 

 older working 

 naturalists, but 

 the characters 

 given for the 

 creatures im- 

 mediately upon 

 exclusion from 

 the egg were 

 vague and un- 

 satisfactory. 



The eggs, as is 

 well known, are 

 laid side by side 

 in somewhat 

 regular patches 

 on reeds, palings, 

 etc., and are of 

 the form shown 

 in the accom- 

 panying figure 2. 

 The micropylal 

 capsule is very 

 prominent in these eggs 

 most noticeable feature. They are of a dull brown 

 colour until ripe for the emergence of the early 

 larvae, when the larval pigment shows through 

 the egg-shell, causing it to appear reddish in 

 colour. After hatching, the egg-shell becomes 

 semi-transparent. Being dense during incubation, 

 it is almost impossible to gain any idea of the 

 embryological phases. Certain of them, however, 

 are clearer than others, and I was fortunately 

 enabled to examine microscopically a specimen 

 (the one figured) in which the outlines of the 

 almost-ready-to-be-excluded larva were faintly 

 visible. Beyond this I was unable to make obser- 

 vations on the larva in ovo. 



Fig. 1, group of eggs of Sialis. Fig. 



F'g- 4. 



Fig. 3, larva immediately on exclusion from egg, magnified 



larva in second stage. c and c? pulsating corpuscle 



lines / indicate natural size. 



and is perhaps their 



In the examination of the excluded larva I had 

 better fortune. Turning over some of the eggs from 

 which I knew the larvae not to have emerged, my 

 attention was attracted to several minute reddish 

 spots apparently taking the places of the capsules. 

 On closer observation I found the capsule in each 

 case pushed aside and the minute larva struggling to 



free itself from 

 the now useless 

 egg-shell. This 

 being accom- 

 plished, in about 

 ten minutes a 

 spasmodic move- 

 ment took place 

 in the hindmost 

 segment, prob- 

 ably as a means 

 of extension 

 thereof to prepare 

 the creature for 

 its slightly later 

 form. At this 

 stage the larva 

 (making some 

 allowance for dis- 

 tortion caused 

 by pressure in 

 mounting the ob- 

 ject in balsam on 

 a micro slide) is, 

 as shown in fig. 2, 

 altogether lumpy 

 and inelegant. 

 In the living 

 creature under 

 the microscope 

 a systolic and 

 diastolic action of a large red corpuscle situated 

 in the thoracic region was at this stage very dis- 

 tinct, but I failed to observe a circulation of fluid 

 either therefrom or in the hardly visible vascular 

 system. The body seemed almost unsegmented, 

 and was apparently destitute of the branchiae 

 so easily seen in all the later larval stages. The 

 body is also sparsely haired. The tail is seen as a 

 tubular projection situated between two humps on 

 the immediately preceding body segment. The 

 legs are doubtfully situate in the thoracic region. 

 One of the most noticeable features at this stage is 

 the mandible, which is of the bidentate form shown 

 in the figure, the outer tooth, however, being 

 stouter and shorter than the inner. Possibly 



magnified, showing embryo. 



The 



