448 NOTES AND MEMORANDA. 



cHrection, since the same individual sometimes directs itself towards the 

 light, and sometimes away from it. In the movements here spoken of, 

 the colourless portion which bears the cilia is always directed forwards. 

 It depends on the i:)ower of the light whether the forward or the back- 

 ward movement is the more rapid ; if the light is feeble, the forward 

 movement is almost always the most marked, and the contrary when 

 the light is strong. 



The final result will therefore be, that after some time, in the one 

 case, the zoospore will approach the light, and in the other it will go 

 away from it. The intensity of the light has moreover an influence 

 on the ulterior movements, since mobile spores of the same species, 

 which have attained the same phase of development, will behave 

 differently under the same conditions of light, depending on whether 

 they have been previously kept for some time in darkness, or on the 

 contrary exposed to a strong light. 



The sudden removal of the source of light which determines the 

 direction of the movement of mobile spores is immediately shown 

 by the abandonment of the direction 2'>i'eviously followed ; in many 

 cases the forward movement ceases suddenly. This phenomenon is 

 produced in both phases of the periodic movement, that is to say, in 

 the individuals which are at the moment directed towards the light, 

 and in those which are moving in the opposite direction.* 



Entophytic and Entozoic (parasitic) Species of Cryptogams. — 

 P. F. Eeiusch contributes to the ' Botauische Zeitung,' f an accoimt 

 of the parasitic Algfe and Fungi which he has himself detected as 

 growing within the tissues of animals and plants. Those hitherto 

 observed as entozoic within the bodies of living animals belong to the 

 lowest classes of Algae and Fungi, viz. Phycochromacese, OscillatorieaB, 

 Leptothrichete, Schizomycetes, and Hyphomycetes, and especially to 

 the genera Protococciis, Pleurococcus, Gkroococcus, Sarchia, Vibrio, 

 Spnillum, and Bacterium. In addition to these he records the 

 following: — 



1. A Floridea parasitic on Sponges and Bryozoa. — This has been 

 detected by M. Eeinsch in the form of red threads, growing within 

 tlie tubes of sjionges and of Sertidaria pluma, the latter itself growing 

 on some of the large Fucacete of the Atlantic coast. The parasite 

 enclosed within the thallus of the sponge forms elongated, usually but 

 slightly branched threads, isolated or collected into bundles, pene- 

 trating the medullary and cortical substance of the sponge, never 

 breaking through to the outside. No reproductive organs were de- 

 tected. The parasite found within the tubes of Sertularia and Tubu- 

 laria was different in form. It occurs as a weft of branching filaments 

 covering the interior of the tubes, some of the filaments penetrating 

 through the tissue of the tubes themselves. The reproductive organs 

 occur in the form of tetrasporangia placed on short unicellular or 

 bicellular pedicels, which were found only in the Sertularia and not 

 in the Tubularia. These indicated a close afiinity on the part of the 

 parasite to Callithamnion. 



* 'Eov. Internrit. Sci.,' iii. (1879) 66. t xxxvii. (1S79) 17 and 33. 



