NOTES AND OBSERVATIONS ON BOARD H.M.S. RATTLESNAKE 



can say positi^•ely, as the result of recent careful examination, that 

 Spongilla, Halichondria, and Grantia are entirely composed of nucleated 

 cells. 



The Foraminifera and Sponges then, no less than the Infusoria and 

 Gregarinidse, are " unicellular " animals— animals, that is, which either 

 consist of a single cell, or of definite aggregations of such cells, none 

 of which possesses powers or functions different from the rest. 



Using the word " unicellular " in this extended sense (as it has 

 been used by Nageli and others ^\■ith regard to the Alga;), it may be 

 said that there are four families of unicellular animals ; in two of these, 

 the Infusoria and Gregarinidae, the cells are isolated ; in two, the Fora- 

 minifera and Sponges, they are aggregated together. 



From these considerations it appears to me that the zoological 

 meaning and importance of the ThalassicoUa punctata first become 

 obvious. It is the connecting link between the Sponges and the Fora- 

 minifera. Allied to the former by its texture and by the peculiar 

 spicula scattered through the substance of some of its varieties, it is 

 equally connected with the latter by the perforated shell of other 

 kinds. If it be supposed that a ThalassicoUa becomes flattened out,, 

 and that a deposit takes place not only round the cells, but between 

 the partitions of the central " vacuola;," it becomes essentially an 

 Orbitoides?- 



To come to a similar understanding of the nature of the Thalassi- 

 coUa nucleata, it is necessary to recur again to certain general char- 

 acteristics of the reproductive processes in the unicellular animals. 



If we except Tethya,di sponge,^ the ordinary reproductive elements 

 have as yet been found in no unicellular animal. 



Fission occurs in all except perhaps the Gregarinidae. Gemmation 

 appears to take place in the Foraminifera and Infusoria. In the 

 Sponges the so-called ova or gemmules seem to be only a temporary 

 locomotive condition of the cells, such as occurs in the Vorticellce 

 among the Infusoria, and the Protococci among plants. 



But in all (except the Foraminifera) a process of multiplication by 



^ Dr. Carpenter, to whom I communicated these observations, writes to me : " As far as 

 I can understand them, the bodies described (if perfect non-embryonic forms) seem to con- 

 stitute that kind of connecting link between Sponges and Foraminifera, which the relative 

 position I have assigned to them would lead me to expect. It is interesting to remark that 

 the cuUender-like skeleton of certain Foraminifera is extremely like in its appearance to a 

 fragment of the shell of an Echinus, or to the plates contained in the integument of a Holo- 

 thuria, and we know that these begin with a network of spicules. Consequently there is not 

 by any means so great a distinction between the spicular skeleton of a sponge and the 

 cullender-like skeleton of an Orbitolina as might at first sight appear." 



^ See Annals of Nat. History, S. 2, vol. vii. p. 370. 



