72 SUMMARY OF CURRENT RESEARCHES RELATING TO 



lamella ; the migration continues, and their number increases. The 

 migi'ation would seem to be passive, and dependent on the stream of 

 nutrition which enters from the endoderm. Cultivation-experiments 

 led to the conclusion that we have to do here, as also in Spongilla and 

 ParamtBcimn, with the lowest unicellular algae, which multiply by 

 tetrad-formation; starch-granules as well as chlorophyll (and a 

 nucleus) may be made out in their interior. Basing himself on these 

 observations, the author feels justified in expressing a belief that 

 whenever chlorophyll is found in the animal kingdom we have to 

 do with green algae, which live in the animals. 



Prof. E. Eay Laukester * lodges a protest against the reception of 

 Mr. Hamann's conclusions as reasonable, and repeats the views he has 

 previously expressed "j" that there is no more and no less evidence for 

 considering the green corpuscles of Hydra viridis as parasitic algae 

 than there is for taking a similar view with regard to the green 

 corpuscles in the leaf of an ordinary green plant. 



Development of the Ovum of Podocoryne carnea. | — In this 

 species, A. de Varenne has already shown that the ova do not originate 

 in the interior of the Medusa, but in an endodermic cell of the 

 ccenosarc of the hydra-polyp itself. This cell differentiates and then 

 passes into a diverticulum, which, developing, becomes a Medusa. 

 This Medusa detaches itself from the polyp, and swims free, carrying 

 the ova, which occupy the walls of the manubrium and there arrive at 

 maturity. He now describes the development of these ova, few obser- 

 vations only having hitherto been made on the species with free 

 Medusae, and as the result concludes that, in Hydroida which have a 

 free Medusa, the ovum presents the same development as in the 

 species which have sporosacs that remain always attached to the 

 colony. 



' Challenger ' Deep-Sea Medus8e.§ — The deep-sea Medusre, which 

 are described by Prof. E. Haeckel, form one of the smallest and least 

 important groups of the rich and remarkable deep-sea fauna discovered 

 during the voyage of the ' Challenger.' The number of species 

 described does not exceed eighteen, of which half are Craspedotae and 

 half Acraspedee. They were briefly diagnosed in the ' System der 

 Medusen' in 1879, || but they are here described at great length and 

 with a most splendid series of illustrations. The descriptive portion 

 of the memoir is prefaced by a very elaborate sketch of the com- 

 parative morphology of the Medusae, which is illustrated by many 

 woodcuts. 



It would seem by no means certain that all the eighteen species 

 are constant inhabitants of the deep sea. The method of capture by 

 the tow-net, by which such delicate and fragile organisms are brought 



* Nature, xxvii. (1882) pp. 87-8. 



t Quart. Joura. Micr. Sci , xxii. (1882) pp. 229-54. 



X Comptes Eendus, xciv. (1882) pp. 892-4. 



§ Reports on tlie Scientific Results of the Voj-age of H.M.S. 'Challenger' 

 during the years 1873-6, vol. iv. (1882) cv and 151 pp., 32 pis. and 15 tigs. 

 Cf. Nature, xxvii. (1882) p. 74. 



II See this Journal, iii. (1880) p. 272. 



