72 PROCEEDINGS OF THE ACADEMY OF 



that tli c female flowers in coniferous plants were borne only on the strong 

 vigorous shoots. These vigorous shoots would in time be crowded and weak- 

 ened by shade, when they would cease to bear female, and produce male 

 flowers only. 



Prof. Cope suggested that, without reference to the relative vigor of the 

 shoots, the male flower was below, and the female flower above; in these 

 Docks the female flower was below, and the male above. 



Mr. Meehan said he had never placed any value on relative position, unless 

 relative vigor went with it. In the case of coniferous trees, Pimis particu- 

 larly, the male flowers were evidently partially formed the fall before ex- 

 pansion, and at the same time that bud scales were forming, and growth 

 forces nearly at rest for the season. They were still in the weaker position, 

 although appearing at the base. 



Prof. Leidy remarked that the interesting communication of Mr. Meehan 

 had recalled to his mind a result of his experience, which he thought would 

 accord with that of others, viz : that species viewed as common to both 

 Europe and America frequently exhibit slight peculiarities, which are dis- 

 tinctive of those of the two countries. It is what might be inferred even if 

 we admit the evolution of existing species from a common remote ancestry. 

 A wide separation, with a considerable lapse of time and a modification of 

 circumstances, are sufficient to account for the slight and acquired differences. 

 Even where differences are not observed in form and structure, they may exist 

 in the habit of the species. Thus the common wolf of Europe and America, 

 viewed by many naturalists as of the same species, differs strikingly in charac- 

 ter in the two countries. In the former it is a more fearless animal, not hesi- 

 tating to attack man ; in the latter, it is said never to attack man. 



At an early period observers saw, or thought they saw, many of the same 

 species of plants and animals indigenous to America that occur in Europe, 

 and hence the common names of European species were applied to those of 

 America. Gradually the list of species common to the two countries was 

 much reduced, and now is comparatively small. 



As might be anticipated, in descending in the scale the species common to 

 the two countries become more frequent; nevertheless many of these common 

 species exhibit geographical peculiarities, which by some naturalists would be 

 regarded as sufficient to consider them distinct. The singular rotifers Meli- 

 crrta ringtns and Limnias ceratophylli are described by European authors as 

 being most general]} 1 - solitary. Here they frequently occur in compound 

 bunches, up to several dozen in a bunch. Agassiz observes : " In the Ameri- 

 can Hydra, as in the European, there are two types, the brown and the 

 green. The American green Hydra, unlike the European, has the power of 

 extending its body in a remarkable degree. Our brown Hydra has very short 

 tentacles, while the P^uropean has long ones." Agassiz views the differences 

 mentioned as characteristic of adifference of species, and names the American 

 green Hydra II. gracilis, and the brown one //. earned. Ayres indicates a 

 brown Hydra, in California, which he says differs from the latter " in the same 

 point and to about the same degree as carnea differs from fit sea." He names 

 this one II. tenuis. "Whilst ready to admit the existence of the peculiarities in 

 these different Hydrse, I do not feel so ready to regard them as distinctive of 

 species, unless the principle is adopted of viewing each peculiarity in a plant 

 or animal as distinctive of species. I have long been familiar with both green 

 and brown Hydra' in the vicinity of Philadelphia, but I have not been able to 

 satisfy myself that they are distinct from Hydra viridis and Il.fusea, two of 

 the four species usually indicated as found in Europe. Our brown Hydra is 

 very common, ami may be obtained on the under side of stones in the Dela- 

 ware and Schuylkill, or on the submerged stems of plants. Though ordinarily 

 its arms appear no longer or shorter than the body, I have seen them elongate 

 atter some davs of rest in a glass vtssel of water to three or four times the 



[July, 



