INVERTEBBATA, CRYPTOQAMIA, MICROSCOPY, ETC. 463 



at the lower part of the stem. The hydrothecsB may become almost 

 opposite. 



Au axillary calycle is a peculiar and constant occurrence between 

 the branch and the stem ; in position, it is alternate with the cell next 

 below it, and on the same side as that next above it in its own inter- 

 node. The cells are more free than in S. cupressina only in internodes 

 of the first and second order. The inclination to form internodes of 

 a high order is less than in S. immila. Gonothecce have been found 

 in S. tenera, but only in colonies much smaller than those of S. cupres- 

 sina — these may be only 30 mm. in height. 



The results of M. Winther's observations convince him that the 

 four species are so closely connected together in pairs, that they must 

 be reduced to two ; thus S. pumila Linn, with gracilis as a dwarf 

 variety, and S. cupressina Linn, with variety tenera, alone remain ; and 

 it must be concluded that the tendency to develop the stem at the 

 expense of the internodes is no basis for distinguishing species. 



As to the homologies and morphological importance of the inter- 

 nodes in their simple or compound state, the study of young colonies 

 and basal i)arts shows the compound ones to arise from obliteration of 

 joints between simple ones. The transitions from one order to another 

 are not abrupt. Internodes of the first order appear in S. cupres- 

 sina only as leading up to those of higher orders. ■ Their /on?* depends 

 on whether the develojiment is uninterrupted in its comjiletion or not ; 

 in the latter case the internode may be finished before a cell is added 

 to the stem ; in the former, new cells keep appearing before the next 

 joint is formed. After an active period like this last, exhaustion 

 appears to set in and a joint terminates the internode. The production 

 of cell-less internodes is explained by the independent development 

 of the stem and the cells, the former being developed earliest. 



Blastology of Hydra.* — Dr. Haacko commences with a short 

 account of the sj)ecific characters of the members of the genus Hydra. 

 He says that he has taken great trouble to try and find the specific 

 names for the not-green Hydrce which he has had in hand ; but the 

 work has been vain. A revision seems to be needed, for the pecu- 

 liarities on which species have been founded are variable, and this 

 applies to the number and length of the tentacles, to the form of the 

 body, and the position of the buds, as much as to the colour. The 

 author has found one point which he thinks to bo of importance ; in 

 the buds of one species all the tentacles appear simultaneously, while 

 in the other only two — and those two opposite to one another — a])])ear 

 together, and the rest gradually sjtring uj) separately. As he has to 

 give new names to these two, he calls the first //. Tremhleyi, and the 

 second II. liocsclii (after Riisel von Eosenhuff) ; the third species of the 

 genus is //. viridis. 



Tlio jiaper will only be, however, intelligible to those who arc 

 acquainted with every term employed by Trufessor ilaeckfl, and by 

 those wluj go even further than he ; the rest must bo contented to 

 kuow that l)r. llaacke finds that the remarkable mode of development 



• 'Jin. Zcitsclir. Naturw.,' xiv. (1880) p. 133. 



