550 



NATURE 



\Oct. 7, 1880 



of water, which is generally the case when the task is intrusted 

 to a subordinate, it is sometimes next to impossible to concen- 

 trate the fluid enough to show the results with the desired 

 plainness. , „ . , . 



" Returning home, we poured the fluid mto soup-plates set on 

 a tible before a window. The diatoms speedily settled on the 

 sides and bottoms of the plates coating them with a green 

 slime, the thickness and tint of which varied with the proportion 

 of diatoms present. In each plate, according to its size, we put 

 three to six perfectly white oysters « hich had never been in the 

 'clears,' and the shells of which had previously been washed 

 and brushed clean. In similar plates like numbers of the same 

 oysters were laid in ordinary sea-water. Twenty-six hours after 

 the commencement of the experiment the oysters in the water 

 charged with diatoms had all acquired a marked greenish hue : 

 the other oysters remained unaltered. The experiment was 

 repeated many times with identically the same results. The 

 o-reen colour in the oysters was found to be more decided in pro- 

 portion as the water was more highly charged with diatoms. In 

 the course of the experiments the shell of one of the oysters was 

 perforated, so as to lay bare the mantle. After the oyster liad 

 turned green, it was laid in ordinary sea-water for a few days, 

 when the greenness disappeared altogether. It reappeared when 

 the oyster was replaced in fresh water containing Namciila 

 cslrearia. The experiment was repeated, with like results, in 

 the laboratory of M. Decaisne, Jardin des Plantes, Paris, to 

 which a supply of white oysters and sealed flasks of the water 

 containing the diatoms was forwarded. 



" In the course of the experiments it was observed that by the 

 opening and closing of their valves the oysters induced currents 

 in the water, by means of which they drew towards them and 

 surrounded themselves with the particles of matter suspended 

 therein. The existence and direction of these currents were 

 shown by the disappearance of the slime and the consequent 

 l.iying bare of the sides and bottoms of the plates, the diatoms 

 remaining only at points out of reach of the currents. 



" Directed towards the buccal aperture by the cilije with which 

 the branchiae are provided, the naviculae enter the stomach of the 

 mollusc, and there part with their nutritive constituents. The 

 yellow chlorophyll is digested and decomposed ; the soluble 

 colouring matter passes direct into the blood, to which it im- 

 parts its colour. Thus it happens that the most vesicular por- 

 tions of the structure, as the branchije, are the most highly 

 coloured. 



"Examination of the digestive tubes of the oysters experi- 

 mented upon proved the fact of the absorption of the diatoms. 

 The stomachs, intestines, and exuvia; were strewed with cara- 

 paces of naviculce. The carapaces, being siliceous, are not 

 affected by the digestive juices, and it would seem extraordinary 

 that with so tenacious a covering their contents should be evolved, 

 w ere it not for the knowledge of the fact that the covering is not 

 continuous, the line of suture separating the valves composing 

 the frustule being scarcely silicified at all." 



It would therefore appear to be established beyond dispute 

 that the green hue in oysters is due exclusively to tlieir absorption 

 of certain naviculre contained in the circumambient water. The 

 facts are in perfect keeping with the observations of growers 

 that heavy rains (which increase the supply of fresh water) cause 

 the disappearance of the green from the " clears," while, on the 

 other hand, dry north-east gales, which greatly increase the 

 saturation of the water, bring it, as it is called, "into condition." 



Two points of special interest in connection with the subject 

 remain for future investigation. These are: — 



1. Does the navicula in question remain all the year in the 

 waters where it is found in winter ? 



2. Is the coloration of the beds accidental or temporary ? — in 

 other words, does this alga disappear from the reservoirs when 

 the water changes its coloiu', or does it become itself discoloured 

 for a time ? H. M. C. 



MODERN ENTOMOLOGY^ 

 T T is the good fortune of your president on this occasion to 

 -*• welcome you to his native heath, where our favourite science 

 has been longer, more uninterruptedly, and perhaps more 

 zealously cultivated than anywhere else in the New World. 

 Here, in the last century. Peck studied the Canker-worm and the 



» Annual Address before the Entomological Club of the American Associa- 

 tion for the Advancement of Science, by the President, Mr. S. H. Scudder, 

 of Cambridge. 



Slug-worm of the Cherry, and in Ute years Rhynehicntts, Steno- 

 corns, and Cossiis — all highly destructive insects. Here lived 

 Harris, who cultivated entomology in its broadest sense, and 

 whose classic treatise was the first important Government publi- 

 cation on injurious insects. Here to-day we have two associa- 

 tions for our work, consisting, it will be confessed, of nearly the 

 same individuals, and not many of them, but meeting frequently 

 — one in Boston, the other in Cambridge, Harvard acknow- 

 ledges the claims of our study in supporting not only an 

 instructor in entomology at its Agricultural School, but a full 

 Professor of the same in the University at large. 



In our own day the spreading territory of the United States, 

 the penetration of its wilds, and the inersection of its whole 

 area by routes of travel, the wider distribution and greatly- 

 increased numbers of local entomologists, as well as the demand 

 for our natural products abroad, have set before 7is temptation 

 to study only new forms and to cultivate descriptive work, to'the 

 neglect of the choicer, broader fields of our ever-opening science. 

 It is this danger to which I venture briefly to call your attention 

 to-day, not by way of disparaging the former, but rather in the 

 hope that some of our younger members, who have not yet fallen 

 into the ruts of work, may be induced to turn their attention to 

 some of the more fruitful fields of diligent research. 



We should not apply the term descriptive work merely to the 

 study of the external features of insects. The great bulk of 

 what passes for comparative anatomy, physiology, and embryo- 

 logy is purely descriptive, and is only to be awarded a higher 

 grade in a scale of studies than that which deals with the external 

 properties when it requires a better training of the hand and eye 

 to carry it out, and greater patience of investigation. We pass 

 at once to a higher grade of research when we deal with com- 

 parisons or processes (which of course involve comparisons). All 

 good descriptive work indeed is also comparative ; but at the 

 best it is so only in the narrowest sense, for only intimately 

 allied forms are compared. In descriptive work we deal with 

 simple facts ; in comparative work we deal with their colloca- 

 tion. "Facts," said Agassiz one day, "factiar stupid things, 

 until brought in connection with some general law." 



It is to this higher plane that concerns itself with general laws 

 that I would urge the young student to bend his steps. The 

 way is hard ; but in this lies one of its charms, for labotu" is its 

 own reward. It is by patient plodding that the goal is reached ; 

 every step costs and counts ; the ever-broadening field of know- 

 ledge exhilarates the spirit and intensifies the ambition ; there is 

 no such thing as satiety — study of this sort never palls. 



It is hardly necessary to point out that so-called systematic 

 work never reaches this higher grade unless it is monographic ; 

 unless it deals in a broad way with the relationship and general 

 affinities of insects. It is not my purpose to call .attention here 

 to the needs of science in this department, as they are too patent 

 to escape observation ; but if one desires a model upon which 

 to construct such work, one need not look further than the 

 " Revision of the Rhynchophora," by Drs. LeConte and Horn. 

 Rather than linger here we prefer to pass directly to some of the 

 obscurer fields of study. 



When we compare the number of insect embryologists in 

 America with that of their European colleagues, the result is 

 somewhat disheartening and discreditable ; although perhaps 

 the comparison would be not quite so disproportionate were 

 some of our students to publish their notes. But take all that 

 has been done upon both sides of the water, and what a meagre 

 showing it makes ! Of how many families of Coleoptera alone 

 have we the embryonic history of a single species ? 



In following the post-embryonal history of insects there is 

 work for all. 'While allied forms have in general a very similar 

 development, there are so many which are unexpectedly found to 

 differ from one another, that every addition to our knowledge of 

 the life histories of insects is a gain, and they are to be praised 

 who give their close .attention to this matter. Here is a field any 

 entomologist, even the most unskilled, may cultivate to his own 

 advantage and with the assuiance that every new history he 

 works out is a distinct .addition to the science. The importance 

 of an accumulation of facts in this field can hardly be over- 

 estimated, and those whose opportunities for field-work are 

 good should especially take this suggestion to heart. Nor, by 

 any means, is the work confined to the mere collection of facts. 

 How to account for this extraordinary diversity of life and 

 habits among insects, and what its meaning may be, is one of 

 the problems of the evolutionist. There are also here some 

 specially curious inquiries, to which Sir John Lubbock and 



