INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 585 



histological characters of the Physophoridas. The form under descrip- 

 tion was observed at Trieste, and in nearly all its most important 

 characters agrees with the other species of Halistemma ; of this group 

 it would be one of the smaller representatives, as its whole length is 

 not more than ten inches. The stem, as in all Physophoridfe, is 

 spirally coiled, and this spire follows two directions ; on the axis of 

 the stem and at the base of the tentacles and of the gonophores there 

 are irregularly stellate spots of a red colour, which is most distinctly 

 marked on the male gonophores. 



Our space docs not permit us to enter into the details of this 

 paper, and we must leave it wdth some brief remarks. The swimming 

 bells of this form are noted as being considerably smaller towards the 

 superior pole and the inferior end of the swimming column, and as 

 presenting a bilateral symmetry so distinct that they may well be 

 called dorsal and ventral ; as compared with the body of the Hydro- 

 medusfG, the bell of the Siphonophora displays many very striking- 

 points of agreement, not only in its histological structure, but in its 

 mode of development. In Halistemma the male and female buds are 

 reported as appearing on each tentacle, where they form distinct race- 

 mose groups, placed on a short stalk ; their medusoid structure is 

 feebly develoj)ed ; the male medusoids, which are distinguished by 

 their reddish-brown pigment, are, when mature, set free from the stalk, 

 and for some time swim about freely by the aid of a rich supjily of 

 cilia ; the female buds are, so far as Claus has observed, devoid of 

 pigment ; the egg is relatively large, and has a large germinal vesicle 

 with a nucleolus which is ordinarily homogeneous ; this body always 

 lies close to the distal pole, and appears to leave the egg when this is 

 matured. 



The view that the Siphonophora are polymorphous, first put out 

 by Leuckart, has been opposed by that of Professor Huxley, who 

 regards the various appendages of the Siphonophora as organs of a 

 Medusa ; this latter view has been lately and independently supported 

 by P. E. Miillerand by Metschnikoff ; the processes of development do 

 indeed seem to bear out their conclusions, but Professor Claus points 

 out that the presence of an air-sac, which has a tendency to be reijeated, 

 seems rather to point to the Siphonophore being a complex of self- 

 repeating parts of a Medusa, and therefore to confirm the \iew of the 

 polymorphism of these animals ; the whole difficulty lies perhaps in 

 the conception of the "person " and of the " colony" ; in these forms, 

 as in the Cestodes, the difference is not one that is to be insisted upon, 

 but is one rather that is most marked when they are regarded com- 

 paratively. 



Tubularia mesembryanthemum.* — An exhaustive study of the 

 histology and embryology of this species has lately been made by 

 Ciamician. 



1. Methods. For examination of the tissues as a whole, the author 



recommends treatment with 0-25 to 0-05 per cent, osmic acid; for 



isolation of the separate elements of the tissues, maceration in 1 per 



cent, chromic acid, staining with eosin, and teasing out in glycerine. 



* ' Zeitschr. wiss. Zool.,' xxsii. (1879) p. 323. 



