114 PROCEEDINGS OF SOCIETIES. 



Pkesident, the Eev. J. B. Eeade, Dr. Wallich, and Mr, Hogg 

 joined. 



Dr. Wallich was fully able to confirm the valuable observa- 

 tions of Dr. Collingvvood, having had opportunities of examining 

 and figuring the organisms referred to during voyages to and from 

 Bengal, in the years 1851 and 1857. Although, in common with 

 Dr. CoUingwood, he had never witnessed the blood-red colour, 

 ascribed by some writers to the occurrence of minute algae in the 

 waters of the ocean, he had on many occasions, during protracted 

 calms, seen the normal clearness modified to a considerable extent, 

 and indeed tinged of a yellowish or greenish-yellow hue by in- 

 numerable minute protophytic masses, in some cases consisting of 

 structures allied to the Trichodesmium* of naturalists, in others 

 of true Diatomacese. The former occurred in the Bay of Bengal 

 and Indian Ocean, and were met with from 18° N. lat. to nearly 

 30° S. One form, probably similar to that spoken of by Dr. Col- 

 lingwood, presented itself in minute spherical masses, about gV^'^ 

 of an inch in diameter, composed of filaments radiating from a 

 common centre, each filament consisting of cells, about twice as 

 broad as long, placed in linear series, and filled with a pale 

 yellowish-green endochrome. The other form occurred in fasci- 

 cular clusters, like minute bundles of faggots, from -^oth to n^gth 

 inch in length, compressed or constricted at the centre of the 

 masses, and from the centre spreading out into brush-like expan- 

 sions. In this variety the surface of the filaments was covered 

 with very delicate hairs, but in other respects the filaments and 

 cells were not distinguishable from those in the spherically-aggre- 

 gated form.f 



The Diatomacese alluded to belonged to the genera Rhizoselenia 

 and Cosciuodiscus. The Rhizoselenia occurred in dishevelled tufts, 

 varying in diameter from half an inch to an inch and a half, 

 without any regular arrangement, and looking, whilst floating in 

 the water, like flocculent tufts of delicate yellow silk. The indi- 

 vidual filaments were of great length, being formed sometimes of 

 a series of fi'om twenty to forty frustules. It was whilst examining 

 these in the fresh and living condition that Dr. "Wallich found 

 what he believes has not heretofore been noticed, namely, distinct 

 connecting zones, which were wanting to prove the true diato- 

 macean nature of the lihizoseleniae. These connecting zones are 

 extremely hyaline, and require most careful manipulation and 

 lighting to render them visible under the microscope. They 

 embrace the corresponding halves of adjoining frustules, are 

 devoid of all striation, and from their very delicate nature are 

 at once rendered invisible, or become actually destroyed, on 

 submitting the organisms to the action of acids. Another notable 

 character in this lihizoselenia is afforded by the manner in which 



* See the translation of a paper by M. Dareste, published in Vol. Ill, 

 N. S., 1863, of the 'Societies' Transactions,' p. 1180. 



t Both forms are figured in the Volume of Sketches whicii Dr. Wallich 

 had recently presented to the Society. 



