ZOOLOGY AND BOTANY, MICROSOOPY, ETO. 843 



BJiahdonema arcuaium. The following are the salient features : — 



(1) The male frustules are the smaller in size, have the more definite 

 arrangement of eudochrome, and are the more readily detached. 



(2) The female frustules have slightly longer valves, more numerous 

 annuli, and have always a wide band near the middle. (3) Conjuga- 

 tion is always polyandrous, and is effected by the male frustules 

 attaching themselves indifferently to any part of the annuli of the 

 female frustule. (4) The result of such conjugation is the production 

 of one sporangial or zygospore-frustule if only the basal half of a 

 female frustule persist ; but if both halves persist, each will produce 

 a sporangium — the two sporangia being in close apposition. (5) The 

 sporangial or zygospore-frustule consists of two valves, without 

 annuli, which have a length about thrice that of the valves of the 

 female. With regard to the inducing causes of conjugation, it would 

 appear that self-division, which gradually reduces the size of the 

 bounding valves, has gone on so long that a new generation becomes 

 necessary to maintain the size. 



Sections of Diatoms from the Jutland " Cementstein." * — M. W. 

 Prinz criticizes at some length the opinions expressed in recent papers 

 by MM. Grunow, Deby, Cox, and Flogel, calling in question the 

 results of the researches undertaken by M. Van Ermengem and him- 

 self concerning the structure of the valves of diatoms. He also 

 describes from both a geological and a petrological point of view the 

 Jutland " Cementstein," and the mode of occurrence in it of the 

 diatoms as well as their state of preservation, which he maintains is 

 one of absolutely perfect integrity. The question of illusory images 

 and the visibility of the perforations of diatoms in the sections is 

 discussed, with some observations on perforated and imperforated 

 diatoms found in the rock. He also draws attention to a singular 

 imperforate organism which, according to Dr. Van Heurck, is probably 

 not a diatom, though, like certain diatoms, it is composed of two 

 unequal valves fitting into each other. 



Phytophagous Fishes as Disseminators of Algse.t — Sig. A.Piccone 

 finds in the digestive organs of Box Salpa, portions of as many as 

 eighteen species of seaweed, some of them in a fruiting condition, the 

 spores or conceptacles of which arc evacuated with the faeces ; and he 

 concludes that this is of great importance in the dissemination of the 

 species concerned. 



Lichenes. 



Formation of Thalli on the Apothecia of Peltidea aphthosa.J — 

 Dr. M. Fiiiifstuck describes specimens of this lichen from various 

 localities in which the apothecia, when they had attained a certain 

 Bta^e of development, wore covered on their back by small, wrinkled 

 thallus-scales. A transverse section througli an apotheciuui in which 

 these scales had not yet made their appearance, reveals, in the medul- 



• Bull. Boc. Ikl(,'o Micr., xi. (188.5) pp. 147-93 (4 pis.). 



t Nii)V. Ciiorii. iJ'.t. Ital., xvii. (188.')) pp. I.'J0-8. 



X li'T. DfMitHcli. IJ'.t. f;oHf:ll.. ii. (1884) pp. 447-52 (I pi.). 



