338 



SCIENCE. 



[Vol. XXI. No. 542 



rived from the divisions of the primary mother cell (6). They 

 contain but a small quantity of cytoplasm, and are destined for 

 no further development. After holding the oogonium in place 

 for a time they become disintegrated. The similarity of the 

 nuclei of these cells, in particular the supporting cell &s, to the 

 male nuclei is further very marked. One could easily believe 

 that the nuclear mass which they separate from the egg nucleus 

 becomes replaced by the sperm nucleus. Both cells, b and b^, are, 

 however, not present in all CEdogonmms. The supporting cell 

 (&3) is the only one constantly present, and this is frequently 

 richer in contents, and in one case gives rise to an oogonium. 



In the formation of the Antheridia, there remains a sterile 

 nucleus, the one below the chain of antheria cells, from which 

 these were abstricted. Here alse the similarity to polar bodies is 

 manifest, but, as Strasburger has pointed out, it necessitates that 

 a part of the male branch be compared to a polar body. The 

 author concludes that a morphological conformity is not shown 

 in either case. The process in CEdogonium may be brought in 

 harmony with the theories of fecundation dependent upon polar 

 bodies, but nothing is thus gained. 



The results of this portion of the study can be summarized as 

 follows : Genuine polar-body formation is not present in CEdo- 

 -goniiim. On the other hand, the supposition is not impossible that 

 the two accompanying cells (bi and 63) are the physiological 

 ■equivalents of polar bodies. 



Of the minutia of nuclear fusion in fecundation much remains 

 to be determined. The study lacks the fullness and roundness 

 shown in the work of Guignard. Yet much is added to our 

 knowledge, and our attention is turned to an interesting and 

 promising group of plants for study. 



CLIMATE AND THE VARIATION OF SLUGS. 



BY T. D. A. OOCKERELL, LAS CETJCES, NEW MEXICO. 



The slugs, or naked land-mollusca, — nacktshnaoken, they say 

 in Germany, — are found in nearly every part of the world. Many 

 of the species are extremely variable in color and markings, and 

 these variations, as might be expected, usually have a smaller 

 area of distribution than the species to which they belong. Fur- 

 thermore, as I propose to show in the present article, climate 

 seems to have a marked influence on the variation of these ani- 

 mals, so that the same kind of variety may appear, at two distant 

 spots, under similar environment. 



Facts of this kind have been taken, by those who believe in the 

 inheritance of acquired characters, as valuable evidence in their 

 favor. I do not think, however, that they are so valuable in this 

 connection as some have supposed. To cite a well-known exam- 

 ple, the white color of many mammals and birds in the Arctic 

 regions is undoubtedly correlated with a cold climate, but it is so 

 very easy to see where natural selection comes in, that scarcely 

 anyone would adduce this instance as proof of the oirect influence 

 of climate. So it may be in more obscure cases, where environ- 

 ment seems to directly modify species, that we have not yet found 

 out the way in which natural selection is acting. 



In order to be perfectly clear, I will give some examples in as 

 few words as possible, numbering them separately, so that they 

 may be taken one by one, and considered on their merits. 1 will 

 also attempt to classify them under difi'erent headings, according 

 to the kind of environment. 



(A) Influence of Altitude. 



1. Limax marginatus, Mtiller. This species is widely dis- 

 tributed in Europe. Its ordinary color is gray, with more or less 

 longitudinal banding. In 1883 Lessona and PoUonera described 

 a nearly black variety from high altitudes in Italy, calling it var. 

 rupieola. In 1886 the Eev. A. H. Delap sent me two individuals 

 of this variety from the top of the Reeks, County Waterford, 

 Ireland, 3,300 feet above sea-level. They were at the very sum- 

 mit, miles away from any trees. However, about 100 feet lower 

 down an example of the normal form of the species was ob- 

 tained. 



In this instance it can hardly be doubted that these dark forms 

 originated independently on the Italian and Irish mountains, 

 similar environment producing a similar effect. 



2. Limax maximus, L. The normal colors are gray with black 

 spots and streaks. A blackish variety (v. nubigenus, Bourguignat) 

 is found in the Pyrenees. 



(B) Influence of Latitude. 



3. Parmacella valenciennii, "W. and Van B. Extends from 

 south France to Morocco. In the northernmost part of its range it is 

 reddish-brown, without markings. In the Spanish peninsula the 

 mantle becomes spotted with black (var. punctulaia, Ckll.), and at 

 Gibraltar and Tangiers the slug is conspicuously marked with black 

 (var. maculata, Ckll.). But, curiously, at both the last localities 

 there appears a variety, well marked with black, but dark-olive 

 instead of reddish (var. olivacea, Ckll.j. It is noteworthy that 



he varieties on both sides of the Straits of Gibraltar are alike. 

 The var. olivacea resembles in color P. oUvieri, Cuvier, from the 

 Caucasus, at least as represented by an example in the British 

 Museum. 



4. Arioliniax columbianus, Gould. A large slug found in the 

 Pacific coast region of North America, as far north as British 

 Columbia. In California there is a sub-species, cahfomicus, 

 Cooper, identical in color with columbianus. From British 

 Columbia to California the slug has two forms, one with, the other 

 without, black spots, the ground- color in each being reddish-brown. 

 In British Columbia there is a variety (niger, Ckll.) which is en- 

 tirely black. In Costa Rica the species reappears as a sub-species, 

 costaricensis, Ckll.; dark olivaceous in color. Thus on differ- 

 ent continents two slugs, Parmacella and Ariolimax, each nor- 

 mally rufous, develop an olivaceous variety at the southernmost 

 point of their range. 



(C) Influence of Moisture. 



5. Arion ater, Linne. This is a large slug common in northern 

 and central Europe. Typically black, it varies to reddish, yel- 

 lowish, white, brown, and gray, presenting also some beautiful 

 varieties resulting from combinations of these colors. In England 

 one may find specimens of several different colors in the same 

 locality; but Dr. Leach noticed, as early as 1820, that the whitish 

 and pale yellowish forms were specially to be observed in chalky 

 districts. In Scotland, dark varieties prevail. But on the conti- 

 nent, where the climate is drier, is a brick-red form (var. lamarckii. 

 Kal.) not to be observed on the British Islands at all. This red 

 variety is so common and conspicuous in various localities in cen- 

 tral Europe as to attract the attention of tourists and others who 

 are not usually given to observing slugs. 



At Chislehurst, in England, I found intensely black specimens 

 in damp places. 



It is possible that the black variety of Ariolimax from British 

 Columbia, noticed above, may have some connection with the 

 moist climate of that country. 



(D) Influence of Insular Conditions. 



6. Agriolimax agrestis, Linnfi. The common gray garden-slug 

 of Europe, often mottled with dark-gray or black. There is a 

 black variety found in England (var. niger, Morel.), and also 

 above the zone of cultivation in the Azores, but not in continental 

 Europe. There is also a very dark variety {panormitanus, Less. 

 and Poll.) found in Sicily, and, according to Dr. Simroth, also in 

 Crete. These examples of insular melanism may have to do with 

 the influence of moisture. 



7. Ariolimax columbianus, Gould. Specimens found by Mr. 

 Hemphill on Sta. Cruz Island, off California, were paler than the 

 type, being uniform light-straw color (var. straminea, Hempb.). 



8. Amalia gagates, Draparnaud. As its name indicates, this 

 slug is typically black, but in England it is nearly always lead- 

 gray (var. or subsp. plumbea, Moq ) or brownish, very rarely 

 black. In Sicily there is a large black form (var. similis, Ckll.), 

 closely related to the great black sub-species mediterranea, Ckll., 

 of Algeria. Here, as with Parmacella. we see similar or identical 

 varieties on opposite sides of the Mediterranean. In Madeira, 

 there is a dark-brown variety (var. maderensis, Ckll.). In Ber- 

 muda, where the species has no doubt been introduced, it is of the 

 typical form. In Ascension and St. Helena are closely-related 

 forms allied to subsp. plumbea, and another allied variety (var. 

 tristensis, Ckll.) is found both on Tristan d'Acunha and Juan 

 Fernandez. 



It is difficult to see how the species can have got to St. Helena, 



