6o4 



LECTURE XXXV. 



and which now developes into an anchoring root, and then begin to grow. This ques- 

 tion also has no interest for us just now — we are concerned only with the mobility and 

 irritability. That this can in no way be due to the contained chlorophyll, follows at 

 once from the fact that there are also swarm-spores — those of the Fungi — which 

 contain no chlorophyll ; and in like manner the antherozoids or spermatozoids, like 

 them so far as motility and irritability are concerned though usually very different in 

 shape, are devoid of chlorophyll. Here also I exclude those structures which in other 

 respects resemble swarm-spores in origin and function, in which the movements 

 of translation are produced partly or wholly by alterations in the form of the body, 

 and where we have thus to do with creeping movements, the typical form of which, 

 moreover, we shall subsequently consider in the case of plasmodia. Still more 

 definitely to be excluded here are the movements of the Oscillatorise, Bacteria, Bacil- 

 lariae or Diatomacese, and similar cases, since we 

 are still utterly in the dark even as to the preli- 

 minaries with respect to the nature of their move- 

 ment. 



The true swarm-spores and spermatozoa thus 

 do not change their form and size during the 

 movement. They owe their locomotion to certain 

 very minute organs which even at the best and 

 with very high powers are visible only with diffi- 

 culty : these are the so-called Cilia, which may 

 be compared as to form and mode of motion to 

 an oscillating whip-lash, and that is about all that we 

 perceive in them. As a rule, the cilia are situated 

 at the narrower anterior end, singly, or more 

 often in pairs, or fours ; in (Edogoiiiiwi (p. 83, 

 Fig. 79) a circlet of numerous cilia exists at the 

 boundary between the hyaline and green portions. 

 The large swarmers of Vaucheria (p. 108) are 

 covered with innumerable very short cilia, as with 

 a dense pile of velvet. Some spermatozoids also, especially those of Equiseium 

 and the Marsiliacese, possess very numerous cilia, which are also very long. In some 

 small swarmers, e. g. the spermatozoa of the Vaucherise, one cilium is situated at the 

 side, the other on the pointed anterior apex, and in the case of the Euglense so 

 common in foul ponds, and others, there is only a single very long active cilium 

 at the pointed anterior end : in Chytridium, on the other hand, the single cilium 

 is at the posterior end, like a rudder. As an especially interesting case again, 

 mention may be made of the Volvocinese, a subdivision of the Algae : since here- 

 entire cell-families, consisting of 4, 8, 16, 32 or more individuals formed exactly 

 like swarm-spores, make their movements in common because they are held 

 together by a common exceedingly watery delicate cellulose envelope, so that the 

 family constitutes a quadrangular tablet, or a sphere, or an ellipsoid, from the 

 surface of which the long whip-like cilia of the individual elements project in pairs 

 into the water. 



The various arrangements of these minute motile organs, which however 



Fig. 356.— Swarm-spores (Zoospores) a b 

 Acetabularia mediltrranea ; c d of Botrydii 

 grattulatutm (see Fis 2, p. 4) ; ef of Uloth 

 zonata. a b d/zxe. sexual zoospores, or so-tal 

 gametes. 



