SCIENCE-GOSSIP. 



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fill to a certain pitch and then contract, thereby 

 forcing the fluid contained in them into the central 

 portion, which seems to spring into existence 

 when this contraction takes place. It then grows 

 gradually fuller for a time, as the water runs in 

 through the half-contracted radial canals. It then 

 contracts, driving its contents to the exterior, the 

 opening into the radial canals being simultaneously 

 closed up. An inflow of liquid into these canals 

 cause them to fill up suddenly. When they have 

 reached the right degree of fulness they contract, 

 and the process is again repeated. The contractile 

 vacuoles of Paramaecium correspond physiologically 

 with the respiratory excretory, and to a certain 

 extent also with the circulatory system of man and 

 the higher animals. Near the centre of the animal 

 a kidney-shaped or oblong nucleus is situated, 

 and by the centre of this the small, round para- 

 nucleus. 



Reproduction takes place by fission, or by spore 

 formation after encystment. From time to time 

 a process of conjugation appears to be necessary 

 in order that the results of fission may be active 

 and healthy. Two individuals come together and 

 partially fuse. The nuclei are broken up, parts of 

 the paranuclei are interchanged, and new nuclei 

 are formed from the paranuclei. This process is 

 known as " rejuvenescence," and is undoubtedly 

 analogous to sexual reproduction in the higher 

 animals. Paramaecium aurelia is exceedingly com- 

 mon and widely distributed ; it occurs in stagnant 

 pond and ditch water, and may be generally found 

 in water in which leaves have been macerated. 



Paramaecium bitrsaria Ehrenberg, is much 

 shorter in proportion to its length than P. aurelia. 



Fig. n— Paramaecium bursal ia ( x 200.) 



2, zoochlorellen ; cv, contractile vacuoles; », nucleus; 

 »', paranucleus. 



The nucleus and paranucleus are situated in the 

 posterior half of the animal. The arrangement 

 of the mouth, oesophagus and oral groove does not 

 differ much from that of the preceding species. 

 The animal is coloured green owing to the pres- 

 ence of numerous chlorophyllaceous corpuscles 

 Biitschli calls " Zoochlorellen," and which are 



possibly symbiotic algae. The size of the body 

 varies considerably ; 100 microns is, perhaps, the 

 average length. 



The animal occurs in marsh water, and is ex- 

 ceedingly common in the Norfolk dykes. The 

 species was first described by Ehrenberg, and 

 referred by him in "Die Infusionsthiere " to the 

 genus Loxodes ; it was transferred by Foeke in 1836 

 to the genus in which it now stands. 



Family Trachelophyllidae. — " Animalcules free- 

 swimming, ciliate throughout, more or less flask- 

 shaped ; oval and cuticular cilia alike ; the oral 

 aperture perforating the extremity of the narrower 

 anterior region, which is frequently highly elastic 

 and extensile." 



Urotricha lagcnula Ehrenberg, is one of the most 

 simply organized of the Ciliata. It is oval in shape, 

 the posterior end is pointed, and bears a long 

 bristle, which forms the chief characteristic of 

 the genus, and from which the generic name 

 (Urotricha = hairtail) is derived. It is covered all 

 over, except for a small area at the posterior end, 

 with long cilia. At the anterior end is the mouth, 



Fig. 22.— Urotricha lagcnula ( x 335.) 



which is situated at the end of a narrow oesophagus 

 and is capable of much enlargement. At the pos- 

 terior end are the anus and a simple contractile 

 vacuole. A spherical nucleus lies in the middle 

 of the body, but as yet no paranucleus has been 

 observed. The surface is coarsely striated ; the 

 length of the body is from 20 to 30 rrricrons. 



This animal lives in pond and ditch water. It 

 swims slowly, but sometimes makes sudden jumps 

 over a short distance ; the jumping movement is 

 due to a sharp vibration of the posterior hair. 



Family Colepidae. — "Animalcules free-swimming, 

 symmetrically ovate, persistent in form, ciliate 

 throughout; oval cilia slightly larger than those 

 of the general cuticular surface. 



Coleps hirtus Ehrenberg, is barrel-shaped, with 

 one side slightly more convex than the other. The 

 whole body is covered with a hard cuticular exo- 

 skeleton, which divides up by grooves running at 

 right angles to one another. One series of grooves 

 is longitudinal, the other is transverse, and in the 

 grooves rows of cilia and trichocysts are placed. 

 At the bottom of a slight depression at the anterior 

 end we find the mouth, and round it a ring of 



