150 



SCIENCE. 



[Vol. I., No. 5. 



Mollnsks. 



Anodonta fluviatilis. — Dr. Jos. Leidy directed 

 attention to a basketful of living fresh-water mus- 

 sels, Anodonta fluviatilis, collected from ponds in 

 the marl of New Jersey. He had found them on 

 examination to be exceedingly prolific. The preg- 

 nant females have the branchial uteri, as they have 

 been appropriately named by Dr. Isaac Lea, enor- 

 mously distended with perfected embryos. These 

 appear with a cinnamon-brown shell having a con- 

 spicuous spinous tooth or hook to each valve, and are 

 provided with long byssal threads. Wishing to ascer- 

 tain the proportionate amount of embryos, tlie follow- 

 ing calculation was made: in an individual six inches 

 long, the soft parts were weighed, and found to be 

 135.44 grammes. The branchial uteri weighed 64 

 grammes, and the inner gills 7.34 grammes. Suppos- 

 ing the latter to be of the same weight as the outer 

 gills free from embryos, this weight subtracted would 

 leave .56. 66 grammes as that of the embryos, and 

 78.78 grammes as the weight of the rest of the animal. 

 He estimated that there are 1,280,000 young in the 

 branchial uteri of each animal. 



The mussels were infested with many water mites 

 creeping about among the gills, and the young of the 

 same were found embedded in the mantle. The mite 

 appears to be identical with the Atax ypsilophoras 

 described one hundred years ago by Bonz, as infesting 

 the Anodonta cygnea of Europe. It is of a dense 

 black color, with a T-shaped yellow mark on the back. 

 Our Unio complanatus had been found infested with 

 a mite which is probably the Atax Bonzi described 

 by Claparede from European unios. If our parasitic 

 mites are identical with those of European mussels, 

 it not only makes it appear probable that they are of 

 common origin, but renders it the more probable 

 that this is likewise the case with their hosts, even 

 if tliese are not regarded of the same species. — 

 (Acad. nat. sc. Philad.; meeting Feb. 13.) [335 



Insects, 



Luminosity of fire-flies. — Considering the popu- 

 lar interest in the subject, we have very few investi- 

 gations of the light-giving organs of insects ; but for 

 all this, as the latest student of their anatomy, Hein- 

 rich Ritter v. Wielowiejski, observes, there are plenty 

 of contradictory statements. 



The photogenic organs, as Huxley calls them, con- 

 sist of thin whitish plates, resting on the ventral 

 walls of the penultimate and antipenultimate abdomi- 

 nal rings of the abdomen, which is in these spots 

 transparent to allow the emission of the light. In 

 the female glow-worm there are also two small acces- 

 sory light-organs in the last ring. These photogenic 

 plates are composed of ' parenchymal cells,' richly sup- 

 plied with nerves and tracheae. The upper and lower 

 strata of the plates, considered as distinct by former 

 authors, really differ only in the nature of the con- 

 tents of the parenchymal cells above and below. These 

 cells are morphological equivalents of the ' fat-body ' 

 (as maintained by Leydig), and physiologically are 

 glandular. The production of light results from the 

 slow oxidization of materials formed, under control 

 of the nervous system, by the parenchymal cells. 

 The light may continue to shine long after the death 

 of the cells, and therefore is not a property of the 

 living protoplasm as such. 



The stellate ' terminal tracheal cells ' discovered by 

 Schultze have no connection with the production of 

 light, nor are they the ends of tracheae. They belong, 

 in fact, to the matrix, or peritoneal sheath, of the 

 tracheae, which is spread out about the'point where 

 the fine tracheae branch into still finer ' tracheal cap- 



illaries,' which latter want the spiral threads of the 

 tracheal stems. The ' capillaries ' seldom end blindly, 

 but anastomose with each other into a sort of net- 

 work. They do not penetrate into the parenchymal 

 cells, but seem to run over their surface, twining 

 irregularly around them on all sides. Some (or all ?) 

 of the parenchymal cells are connected with fine 

 nervelets. 



The most useful reagent for the study of the light- 

 organs was a solution of osmic acid (from 1 to 0.1 per 

 cent) in which the living insects were immersed, and 

 later transferred to alcohol, or to a mixture of alco- 

 hol, glycerine, and water. 



The eggs were found not to shine by their own 

 light, but as stated by Newport, though he has been 

 contradicted by Owsjannikow, are sometimes ren- 

 dered luminous by an accidental coating of the lumi- 

 nous substance of the light-giving organs, which might 

 easily be ruptured by the pressure of the masses of 

 eggs contained in the abdomen of a gravid female. 



While the luminosity of the adult fire-flies is evi- 

 dently useful in bringing the sexes together, it re- 

 mains to explain the luminosity of the larvae and 

 pupae, which are thus of course made conspicuous to 

 the eyes of insectivorous birds and other animals. 

 Von Wielowiejski suggests that their bite, already 

 known to be poisonous to the snails on which the 

 young fire-flies feed, is to some extent poisonous to 

 the enemies of the latter. If this is the case, or if, 

 as it may be suggested, they are disagreeable to the 

 taste, the light would of course serve as a danger- 

 signal to protect its givers from attack. 



The author finally calls attention to larval or em- 

 bryonic characteristics found in adult Lampyridae. 

 Besides the well-known larval form of the adult 

 female glow-worm, the ' terminal tracheal cells ' are 

 embryonic structures. There is also the occasional 

 occurrence, on the muscular fibres, of remains of the 

 embryonic formative cells, and the presence of the 

 large free cells in the body cavity. 



The paper appears to be the result of careful and 

 reliable study, and, if somewhat diffuse, is still a most 

 valuable contribution to our knowledge of a difiicult 

 subject: it contains, besides the points already men- 

 tioned, a number of observations on the fat-body, 

 nervous system, cuticula, etc. — [Zeitschr. wiss. zooL, 

 xxxvii. 354.) b. b. [336 



VERTEBRATES. 



Integumentary appendages. — Mr. J. A. Jeffries, 

 spoke of the structure of these parts in birds, and 

 compared these with each other and the appendages 

 of other vertebrate groups. Having stated that the 

 same layers of the epiderm could be found in the de- 

 velopment of all the appendages, and that many of 

 the layers seemed to be the result of physiological 

 conditions rather than of morphological value, he 

 passed to a comparison of the appendages. 



Feathers differ from the scutae of the tarsus in that 

 the internal surface of the mucous layer becomes ex- 

 posed to the air; they arise as hemispherical knobs, 

 not as folds ; they may grow upon the scutae ; and the 

 final structures are totally distinct. The supposed 

 scale-like nature of penguin-feathers has, moreover, 

 been proved to be a fallacy. 



Scutae are separated from the scales of reptiles, 

 with which they have have been assumed a priori to 

 be homologous, in that they arise as folds; they have 

 not the complex structure of scales, they shade into 

 the papillae of the plantar surface of the toes, and 

 they may bear feathers. Finally, any point of resem- 

 blance between feathers and scales also exists between 

 the two, and the folds on the tail of the rat or opos- 



