ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 513 



which are remarkable for the irregularity of their form and their 

 length. They are always provided with one or more nuclei, which 

 are always lateral in position, large in size, and attached to the fibre 

 by a delicate sarcolemma. The walls of the Polian vesicles consist of 

 an outer layer of flattened cells, which recall the endothelial lym- 

 phatic cell ; a layer of connective tissue in which the fibres are longi- 

 tudinal ; a layer of circular muscular fibres, which are very long, and 

 have the appearance, when extended, of elastic fibres, in a state of 

 contraction. They present a number of swellings. Within this there 

 is a layer of epithelial cells. 



Hybridization of Echinoidea.*— K. Koehler finds that, at Mar- 

 seilles, the genital glands of most species are mature in March or 

 April. In making experiments, however, it is necessary to assure 

 oneself by microscopical examination that the elements are ripe, 

 and with the crossing experiments it is right to fecundate by 

 their own spermatozoa the ova of the species treated. When the ova 

 of Strong ylocentrotus lividus were fecundated by Sphcerechinus granu- 

 lans, the Pluteus was regularly and perfectly developed. The same 

 happened when the male was Psammechinus pulchellus. When the 

 male was Dorocidaris papillata, the eggs did not pass beyond the 

 blastula-stage, but the spermatozoa used were here somewhat inactive. 

 A female Strongylocentrotus is not always fecundated by a male 

 Spatangus purpureus. Sometimes, however, even the gastrula-stage 

 may be reached. 



Other examples are given, and the whole shows that cross 

 fecundation is possible, within very wide limits, among the species 

 of the Echinoidea ; while the Pluteus derived from the crossing 

 of two regular Echinoids may not differ much from the normal Pluteus 

 of the female in the experiment, there are certainly well-marked 

 differences between the legitimate Pluteus of a Spatangus and the 

 hybrid Pluteus of that and Psammechinus. While the ova of one 

 species may be fertilized by another, the reverse may not hold 

 true. 



Variation in Asterias glacialis.f — Professor Jeffrey Bell describes 

 " six sets at least " of forms of this species. In the simplest there is 

 never, in addition to the median row of spines along the back of each 

 ray, anything more than a single isolated rather small spine on either 

 side. Passing through forms in which there may be a few of these 

 intermediate spines, or a larger number, we get to those in which 

 there is a distinct row on either side of the now less conspicuous 

 median one : two rows may be indicated on either side, or may be 

 conspicuously developed. All the forms selected came from the coasts 

 of Portugal, the Azores, or Madeira. It is pointed out that the 

 character and arrangement of the pedicellariae depends on the distri- 

 bution of the spines, and it is, in conclusion, suggested that in the 

 history of the Asteroidea the next point to work out " is the nature 



* Comptes Rendus, xciv. (1882) pp. 1203-5. 

 t Zool. Anzeig., v. (1882) pp. 282-4. 

 Ser. 2.— Vol. II. 2 M 



