.Mr. H. J. Caiter on Astasia. 15 



1 -6750th of an inch in diameter, and the cilium about four times 

 this length, while in S. alba it is a little less ; but its striking 

 character in all is the presence of these spines. If any in parti- 

 cular, it was this spiniferous monociliated cell which I thought 

 might be the spermatozoid ; but on performing the experiment 

 mentioned, I not only found it more or less charged with indigo 

 in its isolated state, that is, when torn from its connexions, but 

 also saw it afterwards in situ, covering in great plurality one of 

 the spherical sacs of a piece of Spongilla alba which had been 

 broken up and placed under the microscope for observation (fig. 

 13) : so that this monociliated cell cannot be considered a sper- 

 matozoid*, while it evidently belongs to the cortical part of the 

 spherical sacs, as the cells of this part only take in crude mate- 

 rial ; and it is curious also that in all the Spongillce here (Bombay) 

 it should have the same characters. 



Whether the larger monociliated sponge-cells present these 

 two spines anywhere about them, I cannot say, any further than 

 that, if they do exist, I have never been able to discover them; 

 certainly I have seen many monociliated sponge-cells without 

 them. 



The spiniferous, like the other monociliated sponge-cells, 

 present an oscillatory motion in progression, being driven for- 

 wards by the undulations of the cilium, which, closely as Spongilla 

 approaches the vegetable kingdom in many respects, form a de- 

 cided difference, inasmuch as all cilia for progression in the zoo- 

 spores of the Algse, &c., with which I am acquainted are placed 

 in front of these organisms, where, by a whip-like motion, they 

 drag the body to which they are attached after them : on the 

 animal side, however, the cilium of progression may be either in 

 front or behind; thus, in Astasia limpida, Duj., it is placed in 

 front, as in Euglena, 



Astasia. 



As I have had occasion to mention Astasia limpida here, I 

 will take this opportunity of clearing up, as well as I am able, 

 the confusion that exists respecting this genus. 



In the first place, although no two Infusoria can be more 

 alike than Astasia limpida and Euglena when casually observed, 

 as my description and delineations will showf^ yet the absence 

 of chlorophyll and the presence of a stomachal cavity, &c., for 

 the digestion of crude food in the former, and the presence of 

 chlorophyll and absence of a stomachal cavity as well as of all 



* That is, when it takes in food : I do not know what it might have 

 been originally. Some Algal spermatozoids, if they do not become fecun- 

 dating agents, evidently pass into a more advanced form, which would 

 appear to require nourishment fpr its development. 



t Annals, vol. xviii. pi. 6. figs. 45-48, 1856. 



