430 NOTES AND MEMORANDA. 



a most respectful attcDtion ; facts, however, seem to be against him 

 here, and M. Viguier brings some new considerations to our notice ; 

 the fact that Duvernoy in 1837 spoke of "cinq colonnes vertebrales" 

 in Asferias, and that he called the starfishes " serpents a plusieurs 

 corps, et a une seule bouche," is worthy of notice ; much more so are 

 the following points : the general skeleton of no asterid ever presents 

 a regular segmentation, corresponding to that of the ambulacral and 

 adambulacral series, nor are the radial cteca divided in correspondence 

 with the segments of the body as they are in all annelids. As we are 

 on debatable ground we may, as a matter of criticism on the arguments 

 of, and without any desire to object to the final conclusions of M. 

 Viguier, point out that the segmentation of the vertebral column of 

 the adult bird and mammal does not correspond to that exhibited 

 by the episkeletal muscles or spinal nerves, and yet the metamerism 

 of the Vertebrata is as certain as any fact in morphology. 



Ccelenterata. 



Researches into the Hydrozoa. — Professor Glaus has communi- 

 cated * to the Vienna Academy a long and elaborate paper on such 

 forms as he has observed in the Adriatic. 



In tlie hermaphrodite Chrysaora the development of the embryo 

 is effected within the ovary ; the ovarian cells are formed in the lower 

 cell-layer of the ovarian region, the upper layers of which form part 

 of the gastric epithelium and are richly provided with urticating 

 capsules ; as the cells increase in size, they project into the homo- 

 geneous layer which separates the upper from the lower (germinal) 

 portion, and gradually become provided with a stalk, which is formed 

 at the expense of the neighbouring cells, and, later on, with a 

 follicular investment of flattened cells; fertilization is followed by 

 cleavage into two cells of unequal size, and in the succeeding stages 

 of segmentation the spheres produced are also unequal ; at the point 

 where the larger cells are found an ingrowth commences, and the 

 endodermal tube, which raj)idly extends to the opposite pole, begins 

 to be formed ; in the jirimary coelom of the resulting elongated 

 GasiruJa-lavya a clear fluid is developed ; the next succeeding stages 

 could not be observed. 



A point of much interest in the history of this form is that 

 embryonic develojiment goes hand in hand with growth ; in most 

 AcalejjJice cleavage does not commence until the ovum has attained its 

 full size, but in Chrysaora, just as in the viviparous Aphides and in 

 the Polyi)hemida (Cladocera), development commences while the ovum 

 is still very small, and long before it has obtained its full amount of 

 nutrient material, which in the animal under description is obtained 

 from the already mentioned follicular cells. When the blastopore is 

 closed we get a larva of which the two cell-layers are very different 

 in character; the ectoderm is formed of cylindrical cells, richly 

 provided with urticating capsules of three different forms ; the 

 anterior end of the free-swimming larva is much broader tlian the 

 hinder end, and the cilia form a broader fan. 



* 'Deukschr. Acad. Wien,' xxxviii. (1878) 1. 



