8 Dr. G. C. Wallich on the Diatomacca. 



probability were of a similar character to the aggregations of 

 what is called whale-food in the higher latitudes. Each of these 

 Scripts measured about half an inch in length ; but so close was 

 their aggregation, that, by a sudden plunge of an iron-rimmed 

 towing-net, half the cubic contents, from which all water had 

 percolated, generally consisted of nothing but one thick gelatinous 

 pulp. Each individual presented a minute yellow digestive 

 cavity, of the size of a millet-seed, which contained both Dia- 

 tomacere, Foraminifera, and other organic particles. 



If we take into account the numbers of Diatomacea3 and Fo- 

 raminifera that must exist in order to afford even a small inte- 

 gral proportion of the diet of these creatures, the vast renewal 

 of supply that must be perpetually going on, and the equally vast 

 multitude of these Diatom-consumers that yield, in their turn, 

 a source of food to the gigantic Cetaceans and other large crea- 

 tures of the sea, it becomes possible, in some measure at least, 

 to form an estimate of the manner in which the deep-sea depo- 

 sits become accumulated. 



Although no detailed investigations have up to this time been 

 carried out with the special view of determining the bathy- 

 metrical ranges at which the Diatomacere, Foraminifera, and 

 Polycystina of the soundings may be said to live, sundry vague 

 and conflicting opinions have, here and there, been elicited 

 during the recent inquiries into the nature of the sea-bottom, 

 instituted under the auspices of the British, the Dutch, and the 

 United States' Governments. 



These opinions bear reference, however, almost wholly to the 

 original habitats of such Foraminifera and Polycystina as have 

 been traced in the soundings, it being asserted by some that 

 they lived and died at extreme depths, near the positions in 

 which their shells were discovered ; whilst by others it is con- 

 tended that, having passed their lives in the various littoral 

 regions of the ocean, their indestructible remains were gradually 

 borne away by currents toward the situations at which they 

 ultimately rested. 



It is a notable fact, that both in guanos and deep-sea deposits 

 the discoid forms of Diatomacea3 generally preponderate. In 

 some deposits, as is well known, they constitute almost the en- 

 tire silicious element, although frequently mixed with the calca- 

 reous exuvia3 of Foraminifera, which, from their greatly superior 

 size, form a large percentage of the mass. The abundance of 

 Coscinodiscus in the Indian seas has already been adverted to ; 

 and, from observations made by me more recently amongst the 

 Channel Islands, it appears highly probable that this form is 

 the most largely distributed of the pelagic Diatomacea?. 



In contradistinction to the discoid forms, those of Naviculoid 



