224 



HARDWICKE'S SCIENCE-GOSSIP. 



[Oct. 1, 1S67. 



Next within the integument, and between it and 

 the alimentary canal and ovary, are what appear to 

 be two tubes or cords, which may possibly constitute 

 the nervous system. These are well seen in polarized 

 light. Whether there are two ovaries, or only one 

 extending nearly the length of the body, I have not 

 been able clearly to determine; but from the exa- 

 mination of the parts immediately adjacent to the 

 oviduct, and from the fact that an incision made 

 through the integument on one side of the vulva 

 only caused ova to float out from that half of the 

 body, I am inclined to believe that there are two 

 distinct ovaries, as in the case of the common 

 Ascaris. The ovaries appear to consist of fibrous 

 tissue, very different in appearance and structure 

 from that of the outer integument— a difference 

 which becomes strikingly visible by the action of 

 re-agents. Schultze's test, which produces no effect 

 whatever upon the integument, changes this tissue 

 immediately from its natural pale yellow colour to a 

 deep crimson. When a worm has been immersed 

 in water sufficiently long for its body to have become 

 naturally distended and pliant, it should be cut in 

 two with the scissors, and on pressure being applied 

 to the extremity, and steadily continued along to- 

 wards the cut end, the whole of the contents of the 

 body will be forced out from the integument with- 

 out any apparent injury to either. Treatment with 

 acetic acid will render it easy to separate the fibres, 

 or a drop of syrup and a drop of sulphuric acid 

 added to it will change them to the deep red colour 

 already referred to. But perhaps the greatest 

 amount of interest may be said to attach to the ova 

 themselves, which, from their great number and 

 conspicuous colour, must immediately attract the 

 attention of the most casual observer. The number 

 in the different worms which I have had under the 

 microscope I found to range from a few score to 

 upwards of 10,000 ; in colour they are a clear trans- 

 parent brown, and in shape slightly oval, having a 

 major diameter of ^o inch, and a miuor of eio 

 inch. They may readily be obtained for examina- 

 tion, either by pressing out the contents of the 

 body in the manner above described, or by placing 

 the body of the worm in water, bending it nearly 

 double, and then cutting it half-way through with 

 a sharp-pointed dissecting knife ; the ova will then 

 be found slowly but freely to float out through the 

 incision. A small quantity of acetic acid added to 

 the water will be found to hasten the process, and 

 will also be of further service in clearing the ova 

 from certain granules of matter by which they are 

 frequently surrounded. On carefully examining 

 them for the first time, I found that each one was 

 enclosed in a delicate, colourless, membraneous sac, 

 the opposite ends of which were slightly elongated, 

 and furnished with two fine filamentous appendages, 

 fringed or ciliated at their free ends. It is however 

 rather remarkable that nearly all the ova of the 



various worms which I have examined since the 

 first appear to possess only one filament at each end 

 instead of two ; but as to the fact there can be no 

 doubt, since, as the observation was new to me, I 

 made a drawing of what I saw at the time, and 

 called in another person to verify its correctness. 



Fig. 223. 

 a, b, perfect ova. c, ruptured sac. d, ovum escaped, x 280. 



The sacs containing the ova were filled up with 

 a fluid, the nature of which I have been unable 

 to determine. What may be the purpose of the 

 filaments appears to be a question of some interest ; 

 and it has been suggested that, inasmuch as the 

 ova are found and devoured by various insects, 

 within whose bodies they undergo development, 

 possibly the filaments may have a use as a means of 

 attachment, by which the ova are prevented from 

 passing out of their hosts before coming to maturity. 

 But be this as it may, I have observed that by a 

 comparatively slight amount of pressure, the sac is 

 ruptured and the ovum escapes. It is also further 

 to be noted that in every instance of this kind the 

 sac has broken asuuder in the same direction and 

 manner, namely, in the circumference of its minor 

 diameter, thus separating it into two equal parts, 

 each of which in shape bears a curious resemblance 

 to a round-topped smoking-cap with its tassel. The 

 rupture of the sacs was in all probability due to the 

 compression of the contained fluid, so that it would 

 be unfair to infer from this only that an insect 

 would swallow the ovum alone without its enve- 

 lope ; yet I cannot but regret that my endeavours 

 to clear up this point have not been attended with 

 better success. With this end in view, I have for 

 some days past kept an earwig in a closed glass 

 trough in which I had placed some of the perfect 

 ova; but up to the time I left home this evening 

 they remained untouched, although the insect has 

 had nothing to eat for nearly a week ; and having 

 been caught in a London scullery, it is scarcely 

 probable that its aversion arises from any previous 

 experiences of the effects of swallowing the ova of 

 Mermis nigrescens* Surrounding the ovaries, 

 apparently in contact with the ova, and occupying 

 the spaces between them, is what appears— when 

 seen through the integument by transmitted light- 

 to be a quantity of milk-white flocculent material, 



* To save it from death by starvation, the earwig was set 

 at liberty a few days after, the ova remaining untouched. 



