50 Halicystis and Valonia. 



he then made of this form with H. ovalis, he has come to the conclusion 

 that the Neapolitan plant is another species apparently identical with the 

 form described by Zanardini* in the Adriatic as Valonia ovalis. This 

 form, though smaller, much resembles H. ovalis externally, but differs in 

 having a shorter and more blunt stalk, a more uneven outer surface, but 

 mainly in having larger chromatophores of different shape (plate XIII., 

 fig. 5 ). These occur in great numbers, and are of a rather long spindle 

 shape, and are provided in the centre with a single clear pyrenoid, very 

 like the chromatophores of Bryopsis. Its nuclei, however, resemble gene- 

 rally those of H. ovalis. Dr. Schmitz proposes to retain this form under 

 Halicystis, under the name of H.parvula, and calls attention to the fact 

 that similar differences in the chromatophores of different species in the 

 same genus are to be found in Derbesia and Vaucheria. I may be excused 

 for pointing to such a circumstance in justification of my caution in 

 attaching what may be undue weight to evidence based on these characters. 



The collection and examination of Halicystis ovalis recalled to me 

 certain observations I made in 1886 in Grenada on Valonia ventricosa, of 

 which I then obtained magnificent specimens. This remarkable plant, 

 consisting of a cell as large as a hen's egg, and of much the same shape, 

 varying to the shape of a pear (plate xill., fig. 6a) I found growing in 

 fairly shallow water (i to 2 fathoms) attached to Galaxaura lapidescens, 

 and in 5 fathoms water on the rhizoids of A vrainvillea longicaulis (plate 

 XIII., fig. 6b), the latter being much smaller specimens. It resembles 

 Halicystis in consisting of a single great, unbranched cell, and differs from 

 other species of Valonia (except V. Forbesii probably) in this respect. It 

 possesses no stalk like Halicystis, but agrees with Valonia in the pro- 

 duction of rhizoids terminating in tenacula (plate XIII., fig. 7). Its 

 cell-wall is stratified and exfoliates readily (plate XIII. , fig. 10) on cutting 

 it in section, and exhibits faint striation. The chromatophores possess 

 a pyrenoid (plate XIII., fig. 9). In its protoplasmic layer there are both 

 single starch-grains and masses of amylum, as in other species of Valonia. 

 In these respects it shows distinct differences from Halicystis. 



The remarkable point, however, in these specimens (as also in others 

 collected in Bermuda by Mrs. Whelpdale) is the occurrence in them 

 of reproductive organs. Since such organs have been hitherto unknown 

 in Valonia (the so-called ' germ-cells/ figured by Nageli, Kiitzing, and 

 others, being concerned in branching, but possibly also in reproduction) 

 their occurrence deserves detailed description. The cells in question 

 (plate Xill., fig. 8a,&,c,d) have plainly arisen by free cell-formation within 



* Saggio di classif. nat. d. Ficee., 1843, p. 59. 



