146 NATTJKAL HISTOEY SOCIETY OF DUBLIN. 



in a Spirogyra j* and I have myself seen the same slipping-out by a rent 

 in the spinous outer coat of the " Asteridia" in a Mesocarpus, and the 

 commeencment of self- division. Therefore, be the true nature of the so- 

 called "Asteridia" (Shadbold, Thwaites) what it may, there can be 

 little doubt but that the bodies I describe belonging to Penium digitus 

 are of one and the same nature. 



Thwaitesf and PringsheimJ seem to hold that these bodies are not 

 at all formed at the expense of the contents of the cell of the Confervoid 

 in which they occur, and yet they both seem to regard them as of truly 

 parasitic nature. If the former view be correct, they could not be pa- 

 rasites in the strict sense of the word. But here, in the case in question, 

 though these " Asteridia" were with green contents, like the other 

 forms hitherto noticed, the fact of the original contents of the Penium 

 seeming to have become in most instances all absorbed, or if not all ab- 

 sorbed, the residue becoming quite effete and brown, seems to speak for 

 their actual parasitic nature. 



It is true that Itzigsohn has sought to establish that these " Aste- 

 ridia," as well as the very different bodies he calls " Spermatospheeria," 

 are not parasitic, but to be regarded as forming a part of the fructifica- 

 tion of the plants in which they occur : that they, in fact, represent the 

 male element, and that their contents exert a fertilizing influence on the 

 remainder of the contents of the original cell in which they occur; nay, 

 he even circumstantially explains the process by assuming that the 

 spines are tubules through which permeate whatever the influence may 

 be which is supposed to emanate from the " Asteridium" to the remain- 

 der of the contents of the original cell — a curious fertilization truly, 

 which in Penium digitus kills what it acts upon. This fancy seems to 

 find a kind of parallel in Hassal's somewhat similar assumption, that 

 the nucleus in Spirogyra is the male organ, the fertilization of the 

 parietal contents being assumed by him to be effected in some unex- 

 plained way through the agency of the protoplasmic threads radiating 

 therefrom. § But these assumptions need nowadays, I should think, 

 no refutation ; Pringsheim has long demolished several of Itzigsohn's 

 hypotheses. The fact is that, while imagination has' been largely 

 drawn upon to find a reproductive process in Conjugate, the true one 

 has been overlooked and been regarded as simply a fortuitous or insig- 

 nificant act ; because the process of conjugation is so common and so 

 simple, it is ignored, though the many grades and phases, in the various 

 types which it presents, speak loudly, as it seems to me, for an acknow- 

 ledgment of its true significance. 



* " Zur Kritik und Geschicte der Untersuchungen liber das Algen-Geschlecht," 

 46. 



t " Annals of Natural History," vol.xvii., p. 202. 

 X Loc. cit., p. 47. 

 § " British Fresh- water Algae,'' Intr., p. 6. 



