498 SDMMAIJY OF CURUENT RESEARCHES RELATING TO 



similar oxaminatiou of Melosira (Otihosira) arenaria, tlic maiu results 

 of w'liich are given. 



The two tlaiigliter-cclls which spring from the spoutaucoiis division 

 of a parent-cell of Tcrpsinoe do not behave alike ; the larger one 

 divides earlier than the younger one, triads being produced in this 

 way. This was regarded by 0. Miiller as a contrivance by means of 

 which the further division of cells which had attained their minimum 

 size, and which could now only multiply by the formation of auxo- 

 spores, was prevented ; and he looked for a further exemplification 

 of the law in the filamentous diatoms which remain connected after 

 cell-division has taken place. In Melosira arenaria he found a species 

 which presented all the conditions favourable for such an investigation, 

 in which ho was able to determine the relative ages of all the cells in 

 a filament. The investigation was carried on with the aid of drawings 

 prepared by the best homogeneous-immersion systems. 



Leep-sea Diatoms.* — Count F. Castracane adds another con- 

 tribution to our knowledge of deep-sea diatoms, in the examination of 

 the contents of Holothuria from depths of 2511-5274 metres, ob- 

 tained by the ' Challenger ' expedition. He finds these to agree sub- 

 stantially with the residts previously obtained from the contents of 

 Echini from a depth of 2638 metres. In both cases the animals have 

 only a creeping motion, and could feed only on living diatoms grow- 

 ing in the same situations as themselves. The nature of the diatoms 

 and the relation of their specific gravity to that of sea-water, pre- 

 cluded the possibility that they could have sunk to that depth from 

 the surface. One of the Uolothiirice contained enormous quantities of 

 the delicate Sijnedra thalassiotrix, 3-4 mm. in length, and not more 

 than • 01 mm. in breadth, in a perfect condition, while in sea-mud it is 

 never found in any other than a fragmentary state. In the Echini were 

 also many tubes of Bhizosolenia with excessively fragile walls, in 

 which state it has never been found by the writer in sea-mud. An- 

 other proof that the diatoms were swallowed in a living condition 

 was afforded by the fact that one was found in which the endochromo 

 still retained its yellow colom*. These diatoms must therefore have 

 lived at these enormous depths in the sea. 



Fossil Diatoms.t — Count F. Castracane describes diatoms belong- 

 ing to the genera Cyclolella and Epithemia obtained from a calcareous 

 deposit from Spolcto belonging to the Pliocene formation, and of 

 fresh-water origin. The former of these genera was represented by 

 a single species, i^robably new, and perhaps the finest hitherto known 

 belonging to the genus. 



Structure of the Diatom-valve.} — Dr. H. Van Heui-ck, from a 

 study of fragments in highly refracting media, comes to the con- 

 clusion that the valve of the Crypto-raphidefe is generally formed of 

 two layers. The lower layer is composed of a single lamina, and has 



* Boll. Accad. Pont, de' Nuovi Lincei, xxxviii. (18S5); Sess. Deer. 21, 1884, 

 I'p. 4-6. See this Journal, iv. (1884) p. 939. 



t Boll. Accad. Pont, de' Nuovi Liucci, xxxviii. (18S5) ; Sess. May 15, pp. 8-9. 



X Heurek, H. van, ' Synopsis des Diatome'es de Bclgique,' pp. 35-7. Soo 

 Bull. Soc. Belg. Blicr., xi. (1885) pp. 71-3. 



