Oct. 8, 1S74J 



NA TURE 



465 



for not only does the latter present a larger adhesive surface, but 

 the longer claws are more likely to reach beyond the pubescence 

 and the ^bristles, and fasten to the cellular tissue of the leaf 

 beyond. 



In answer to the second question, I can only say that there is 

 nothing exceptional in the power of the larva to withstand the 

 solvent quality of the fluid ; it is, on the contrary, in accordance 

 with the facts known of many species of Muscidre and Kstrida;, 

 some of which, like the well-known horse-bot, revel in a bath of 

 chyme, while others are at ease in tlie intestinal heat of other 

 warm-blooded animals. It is also well known that they will 

 often live for hours in strong liquids, such as alcohol and turpen- 

 tine. 



Conclusion. — To one accustomed to seek the why and where- 

 fore of things, the inquiry very naturally arises as to whether 

 Xanthoptera and Sarcophaga play any necessary or important 

 role in the economy of Sarracenia. Speaking of the Sarco- 

 phaga larva;, Mr. Ravenel asks, " May he not do some service 

 to Sarracenia as Pronuba does to Yucca?" And if so, may not 

 all this structure for the destruction of insects be primarily for his 

 benefit? Can he be merely an intruder, sharing llie store of 

 provision which the plant, by ingenious contrivance, has secured 

 for itself, or is he a welcome inmate and profitable tenant ? Self- 

 fertilisation does not take place in Sarracenia, and the possi- 

 bility that the bristly Flesh-fly aids in the important ! act of 

 pollination lends interest to the facts. No one has witnessed 

 with, greater pleisure than myself the impulse which Dirwin has 

 of late years given to such inquiries ; but we should be cautious 

 lest the speculative spirit impair our judgments or our ability to 

 read the simple lesson of the facts. My own conclusions 

 summed up are : — 



1. There is no reason lo doubt, but every reason to believe, 

 since the observations of Dr. Mellichamp, that Sarracenia is a 

 truly insectivorous plant, and that by its secretions and structure 

 it is eminently fitted to capture its prey. 



2. That those insects most easily digested (if I may use the 

 term) and most useful to the plant are principally ants and small 

 flies, which are lured to their graves by the honeyed path, and 

 that most of the larger insects, which are notattracieJ by sweets, 

 get in by accident and fall victims to the peculiar mechanical 

 siructure of the pitcher. 



3. That the only benefit to the plant is from the liquid manure 

 resulting from the putrescent captured insects. 



[Mr. Ravenel, in making a transverse section near the base of 

 the young leaf, noticed large tubular cells passing down through 

 the petiole into the root, and much of the liquid manure may 

 possibly pass through these into the root stalk.] 



4. That Sarcophaga is a m re intruder, the larva sponging on 

 and sharing the food obtained by the plant, and the fly attracted 

 thither by the strong o3our, as it is to all putrescent animal 

 matter or to other plants, like Slapclia varitxcta, which give 

 forth a similar odour. There is nothing to prove that it has 

 anything to do with pollination, and the only insect that Dr. 

 Mellichamp has observed about the floweis with any frequency, 

 is a Cetoniid beetle, the Enryoniia inclanchoUca. 



5. That Xantlioptera has no other connection with the plant 

 than that of a destroyer, though its greatest injury is done after 

 the leaf has performed its most important functions. Almost 

 every plant has its peculiar insect enemy, and Sarracenia, with 

 all its dangers to insect-life generally, is no exception to the rule. 



6. That neither the moth nor the fly have any structure pecu- 

 liar to them, that enables them to biave the dangers of the plant, 

 beyond what many other allied sp>cies possess. 



ON EVOLUTION AND ZOOLOGICAL FORMU- 

 LATION* 



IN the means which he has at his disposal for expressing 

 the relative values of the facts of his science the 

 chemist has an advantage over the zoologist which cannot 

 be over-estimated. By a chemical rational formula it is 

 possible to express, in a very small compass, facts of 

 composition and decomposition, as well as many of the 

 other relations borne by the constituents of a compound 

 body one to the other. 



. • The substance of a lecture, introductory to the evening class ol Zoology, 

 at King's College, Str.ind. Uy Prvf. A. it. G.irrod, Kel'.ow of St. Johns 

 College, Cambridge. 



In zoology formulation has received bat little applica- 

 tion ; it has been employed to represent dental series and 

 one or two other numerical points only ; the cumbrous 

 method of detailed verbal description being still resorted 

 to in all cases, even when continuous observation has so 

 accumulated facts, that it is almost impossible to retain 

 the grasp of them without some auxiliary appliances. A 

 method of zoological formulation, which, whilst expressing 

 the facts of anatomical structure, attracts the attention to 

 the relative importance of the observed differences, rather 

 than to the details of the differences themselves, is a great 

 desideratum ; and it will be my endeavour on the present 

 occasion to show how such a method can be made to 

 assist in solving a problem so involved as the true 

 affinities of a group of animals whose variable characters 

 are fairly understood. 



But the chemist has the atomic theory as a basis 

 whereon to build ; is there any principle in biology so 

 inclusive as to yield a foundation on which to construct 

 the desired system ? Until the introduction of the theory 

 of evolution and the doctrine of natural selection there 

 was not. As long as the negative hypothesis of " special 

 creation " held sway, the interest attached to the study of 

 the mutual relations of organised beings was nil. No 

 such relation could, in fact, have existed. But now, 

 through the insight into nature arrived at by the all- 

 embracing theories of Lamarck and Darwin — the Daltons 

 of biology — the pedigree of the animal and vegetable 

 kingdoms will form a problem which it will require many 

 generations of the ablest zoologists to solve, even approxi- 

 mately, by the careful correlation of the undigested, 

 unrecorded, and unobserved facts at their disposal. 



Let us stop for a moment to glance at this doctrine of 

 descent, in which, through the struggle for existence, by 

 a process of natural selection, the fittest (for want of a 

 batter term) are said to survive. We may compare the 

 living body of one of the higher animals to a cannon 

 counterpoised on a Palliser gun-carriage, so fixed that it 

 win hit a target situated at 1,000 yards distance. Before 

 firing let marks be so made that the different parts of the 

 whole engine can be afterwards adjusted to their former 

 position. The gun is fired ; the target is struck ; a 

 well-defined perforation or indentation is the result. A 

 second similar shot is arranged for, by re-adjusting the 

 engine with the assistance of the marks previously made ; 

 but on this occasion no direct aim is taken. The gun is 

 again fired ; but this time the target is missed, or it is hit 

 in a different part. Why is this? It is because, in the 

 former of the two firings, by the strain it caused to the 

 whole machine, by the wear it produced in the rifiing of 

 the gun, and by the shght differences in the quality and 

 quantity of the powder, the shot left the muzzle under 

 different circumstances on the two oocasions. The 

 amount of this difference was sufikient, at the long range 

 selected for illustration, to make the alteration in the 

 course taken by the projectile perceptible. An external 

 influence, the wind, is almost certain to have affected the 

 result. This example shows how that minute differences, 

 firstly in internal, and secondly in external circum- 

 stances, are sure to prevent the exact accordance of con- 

 secutive phenomena which might reasonably have been 

 expected to be fac-similcs one of the other. 



As a general inference from cvery-day observation we 

 are similarly led to expect that the offspring of living 

 organisms will resemble their parent forms. But, as with 

 the cannon, there are minor forces which in living beings 

 come into play to produce slight changes in the progeny 

 on all occasions. These changes are likewise of two 

 kinds, depending on the circumstances connected with 

 the parents themselves, and on those acting directly on 

 the offspring from the time of its conception onwards. 

 Amongst the former of these may be included differences 

 in the actual and relative ages of the parents, both of 

 which factors vary with each one of their-prog-ny ; their 



