756 Mr. Frank Balfour Browne [May 9, 



instiucb possessed by the mother in the deposition of her eggs and 

 the extreme sensitiveness of the borer or ovipositor. Although I 

 examined very carefully the plants in the tubs, only twice did I find 

 that the ovipositor had passed right through the sheath and dropped 

 the egg between that and the stem. 



Lapponicus, unlike our other species of Dytiscus, has a very 

 definite egg-laying period, commencing in March and ending in June. 

 From two of the British species I have had eggs in October, Decem- 

 ber and February, as well as in the summer months. 



I collected a number of the eggs, dissecting them out of the leaf- 

 sheaths, and placed them on wet cotton wool in tumblers and watched 

 their development. 



I do not intend to weary you with the details of the development 

 of the embryo, but I wish to point out that the embryo first appears 

 on a part of one side of the mass of yolk — it does not at first occupy 

 the whole length of the egg — and it then extends first backwards and 

 then forwards, and the sides grow up around the yolk until the 

 embryo ultimately encloses it. The nerve-chord does not increase in 

 length with the embryo, and consequently appears to shorten as the 

 embryo extends in the egg. 



The development of the embryo occupies about three weeks in 

 June, but temperature affects the length of this embryonic period. 

 In the case of another species, an egg laid in April matured in three 

 weeks, while one laid in winter took six weeks to hatch. 



Towards the end of the embryonic period the pressure of the 

 embryo in the shell is very great. I accidentally punctured an egg 

 with a needle when turning it over, and immediately a portion of 

 the embryo bulged through, just as the inner tube of a pneumatic 

 tyre tends to bulge through a tear in the outer cover. The pressure 

 is also indicated by the changed shape of the egg during the final 



During the latter part of the egg-period, there are various slight 

 movements of the embryo, but during the last few hours certain very 

 definite movements become noticeable. In the first place, inside the 

 head a spasmodic pulsation is visible, at first at long intervals, but 

 later more or less continuously. I have observed this pulsation in 

 eggs of other water-beetles, and also in those of the dragon-fly, 

 and although I am not sure that the interpretation is the same in 

 dragon-fly and water-beetle, I am satisfied in the latter case the 

 pulsation is really a swallowing process. 



The larvse of all the water-beetles I have examined possess a 

 special sucking apparatus known as a " pharyngeal pump," the use 

 of which I shall describe directly, and in the embryo this pump 

 apparently comes into use to absorb the fluid which surrounds the 

 embryo in the shell ; the embryo merely drinks this up. 



After this sucking-pump begins to work, various other movements 

 of the internal organs can be observed, including peristalsis, and also 



