May 15, 1884 



NA TURE 



69 



other insects several generations produced by parthenogenesis 

 intervene between true sexual generation^. 



The typical case is that of the Aphides, which has been long 

 known ; here there is little dinerence of habit or structure except 

 as regards wings, and possibly the generative organs. 



Some of the Aphides, however, do show modifications in their 

 life-history almost as remarkable as in the case of the Cynipidce 

 mentioned above. Lichtenstein's researches, though vigorously 

 attacked by some French writers, have been confirmed by Kessler 

 and Horvath. He observed that the Aphides, living during 

 summer at the roots of various grasses, become winged in autumn 

 and fly to the trunks of trees, where they produce sexual indi- 

 viduals ; the solitary egg of the female remains dormant in her 

 dried body till the following spring, when it develops into a 

 gall-making aphis, the foundress, peudogyne. This produces 

 viviparous winged young (emigrant pseudogynes), which in June 

 fly back to the grass, lose their wings, and produce fresh genera- 

 tions bv parthenogenetic eggs. This completes the cycle, and the 

 generations distinguished by habitat are often different in appear- 

 ance, even a large number of different forms being sometimes 

 thus connected. For instance — 



Phylloxera quercus (Balbiani) migrates from Qnercus ilex to Q. 

 sessiliflora. 



P. vastatrix, from the leaf-galls to the root of the vine. 

 Teiraneura rubra, from galls on trunk of elm to roots of dog's 

 grass. 



T. ulmi, from elm-galls to roots of maize. 

 Other less perfect examples of heterogamy, such as Cecido- 

 myia and Asearis nigroi'enosa, are well known. 



The current views concerning the probable origin of the phe- 

 nomena of heterogamy and metagenesis may be roughly classed 

 in two groups, one formulated by Leuckart and supported by 

 Claus and Balfour, the other held by Salensky and Brooks. 



Leuckart supposed that alternation of generations is a division 

 of labour in regard to reproduction in which the two chief kinds 

 of multiplication, sexual and asexual, are divided between dif- 

 ferent individuals and generations. 



The other theory is that these phenomena are due to a modifi- 

 cation of metamorphosis, Salensky also stating that ' ' the con- 

 nection between metagenesis and metamorphosis is much more 

 easily seen in Tunicates than in other animals." _ 



If in an animal undergoing a metamorphosis the larva ac- 

 quired the power of producing other individuals by budding, we 

 should have the larval form undergoing finally a change into 

 the adult sexual form. At the same time it is obvious that this 

 is not an indispensable condition ; for the more individuals the 

 larva produced the more incapacitated it would be for future 

 sexual reproduction, so that in all probability there would soon 

 be no development beyond the larval stage. W. K. Brooks, in 

 a recent paper on the subject, alludes to a medusa, Cunina, the 

 hydroid form of which is parasitic on the stomach of another 

 medusa, Turritopsis. This hydroid produces medusa; by gem- 

 mation, but is itself finally modified into a medusa. 



The contrast between this and the mere usual case is thus : — 



This is, however, in no way more strange than the transmission 

 of sexual characters. 



While, however, the case of the Tunicates may be considered 

 doubtful, it will probably not be denied by unprejudiced ob- 

 servers that the phenomena seen in the Insecta are more easily 

 accounted for by Leuckart's hypothesis than by Salensky's. 



It would seem that there could be no ground for saying with 

 regard to the Cynipida;, that in a group of which it is charac- 

 teristic that only the mature forms, and sometimes not even those, 

 are winged — one winged form is the larval condition of another 

 which is smaller, but not otherwise very different, yet this is the 

 case in Dryophanta seutellaris—Spaihegasler iaschenbergi. 



It is probable, then, that these methods of reproduction have 

 not had in all cases the same origin, and, as in several other 

 instances to which attention has been paid during the last few 

 years, the resemblances, which occur in various animals in no 

 way connected but distributed over almost the whole animal 

 kingdom, may best be considered as homoplastic, that is as 

 brought about in different ways under the influence of similar 

 conditions of life. R - N - *-*. 



Cunina 

 Egg 

 I 

 I Larva 



becoming > — < Adult 

 ' adult 



( H-dinary Forms 



Hydra Hydra Hydra 



I I 



Medusa Medusa 



Similarly in the Cestodes it is usually allowed that the Echino- 

 coccus stage consists in the production of a number of individuals 

 in the larval state, not of adults differentiated to meet diverse 

 methods of reproduction. 



In such a form as Doliolum, and indeed generally among the 

 Tunicata, there seems to be more difficulty attending this view. 

 Gemmation does not result in the production of individuals like 

 the gemmating zooid, which by growth become unlike it. The 

 cyathozooid, or the Doliolum with dorsal stolon, not only do not 

 become sexual after a metamorphosis, but they give rise to the 

 ascidiozooid, a form with ventral stolon in no way comparable 

 to the adult of which it is the arrested larva. It seems here 

 more probable that the existence of two methods of reproduc- 

 tion perhaps taking place at slightly different times has led to 

 the selection of two sets of individuals, one better fitted for 

 gemmation, the other for sexual reproduction. We must then 

 suppose that any influence acting for the modification of one 

 generation is transmitted not to the next but the next but one. 



..Huxley's distinction of 1 



1 ot to hoi ' 



THE PARIS ACADEMY OF SCIENCES 



THE yearly public meeting of this body was held on Monday, 

 May 5, under the presidency of M. Emile Blanchard. The 

 proceedings consisted mainly of a detailed statement of the awards 

 made for prize essays or distinguished services rendered during 

 the year 1883 to the various branches of the mathematical and 

 natural sciences, useful arts, and industries. 



In Mechanics the Extraordinary Prize of 6000 francs, established 

 to encourage improvements of all sorts in the efficiency of the 

 French Naval Service was divided, as in previous years, amongst 

 several candidates. For his " Studies on Marine Engines, now 

 in course of publication, M. Taurines received 3000 francs, M. 

 Germain 2000, for his "Treatise on Hydrography," and Capt. 

 A. de Magnac 1000, for his "New Astronomic Naviga- 

 tion," published in 1877. The Montyon Prize, in the same de- 

 partment, was also divided, half going to M. Leon Francq, for 

 his improvements in Lamm's steam traction engine, and half to 

 Capt. L. Renouf, inventor of an instrument intended to simplify 

 the observation of altitudes at sea, dispensing with the necessity 

 of employing artificial horizons and enabling exact calculations 

 to be made without stopping the vessel under sail or steam. M. 

 Jacquemier, inventor of the kinemometer, dynamometer, and 

 other useful appliances, gained the Plumey Prize ; and M. Marcel 

 Deprez the Fourneyron, for his ingenious electric experiments on 

 the Chemin-de-fer du Nord. 



The Lalande Prize, founded by the illustrious astronomer to 

 stimulate astronomical studies in France and abroad, was unani- 

 mously decreed to MM. Bouquet de la Grye, de Bernardieres, 

 Courcelle-Seneuil, Fleuriais, Hatt, Perrotin, Bassot, Bigourdan, 

 and Callandreau, chiefs of the various French expeditions sent to 

 observe the transit of Venus on December 6, 1882. In this 

 branch the Valz Prize was assigned to M. Stephan, Director of 

 the Marseilles Observatory, and discoverer of about 700 nebula;, 

 the positions of over 500 of which he has carefully determined. 



For his extensive labours in the field of Experimental Physics 

 M. Henri Becquerel was rewarded with the Lacaze Prize, the 

 only one given away in this department. 



In Chemistry the Tecker Prize was secured by M. Etard for 

 his numerous researches and publications on organic chemistry. 

 M. L. Cailletet obtained in this branch the Lacaze Prize for his 

 important researches on the liquefaction of gases, and esper ally 

 for his success in, for the first time, demonstrating the possibility 

 of liquefying all the so-called permanent gases. 



In Geology the Grand Prize granted by the Minister of Finance 

 for the best geological description of any region in France or 

 Algeria fell to M. Fontannes for his long and successful re- 

 searches in the Tertiary Basin of South-East France, mnnly 

 embodied in his " Stratigraphic and Pala:ontological Studies of 

 the Tertiary Period in the Rhone Valley." An exceptional award 

 of 2000 francs was also made in favour of M. Peron, author of 

 an extremely important work entitled " Essay on a Geological 

 Description of Algeria." ; 



For his comprehensive monograph on Trichinosis, M. Joannes 

 Chatin, Director of the Government Laboratory at Havre, ob- 

 tained the Barbier Prize ; and MM. G. Bonnier and L. Mangin 

 the Desmazieres Prize for their memoir on the " Respiration and 

 Transpiration of Fungi," both in the department of Botany. In 

 the same department M. Costantin was the successful competitor 



