1002 SUMMARY OF CURRENT RESEARCHES RELATING TO 



spicular walls. Entire sponges are absent, but a number of species 

 may be recognized. All four orders of tbe group arc found ; tlio 

 Tetractinellidee and Lithistids, particularly tbe Megcmorina family, 

 being the most abundant. 



Protozoa. 



Significance of Conjugation in the Infusoria.* — Dr. A. Gruber 

 has been able to convince himself that, with conjugating Infusoria 

 (Paramecium aurelia), the nucleoli of the two individuals copulate 

 with each other. In addition to their union at their anterior parts, 

 the two individuals are united at a point in the hinder third of their 

 body ; to this point there moves from the left and right a nucleolus 

 converted into a striated spindle ; the two bodies touch one another 

 exactly in the bridge of communication, at first only by their apices, 

 and then more intimately. This conjugation brings about an inter- 

 mixture of nuclear substance from both sides, and explains what was 

 enigmatical to us in the phenomena of conjugation, and appears to 

 bring the conjugation of the Infusoria into direct relation with the 

 sexual reproduction of the Metazoa ; there is an intermixture of 

 different germ-plasmas. If these observations be correct, we must 

 abandon the opinion, apparently supported by facts, that the purpose 

 of conjugation is the rejuvenescence of infusoria exhausted by con- 

 tinual division. 



Conjugation of Paramsecium-t — The study of P. caudatum has 

 furnished M. E. Maupas with certain new points with regard to the 

 action of the nucleolus in conjugation. The nucleolus, in each of 

 two conjugating Paramsecia, divides up into a number of parts, of 

 which all except one is absorbed. This one divides again into two, 

 and of these two nucleolar division products, one remains motionless, 

 whilst the second travels with the apposed Paramsecium, and here 

 fuses with the motionless nucleolar product of this individual. The 

 exchange is mutual. The travelling portion is spindle-shaped and 

 longitudinally striated. The new body formed by this fusion then 

 divides up into two, four, and eight. Of these eight parts, three are 

 absorbed, four enlarge and become nuclei, whilst the eighth remains 

 for a time unchanged. Then, when the Paramsecium divides, this 

 last part also divides, one half going with two nuclei into each of the 

 new individuals. At the second division, each of these halves again 

 divides, so that each of the four new individuals possesses a nucleus 

 and nucleolus, both resulting from a mixed nucleolar product. In 

 P. aurelia, this normal condition is attained earlier than in P. cau- 

 datum. The diagram accompanying the paper shows these processes 

 and the various stages in the two species. 



The period of conjugation at a temperature of 24° C. lasts about 

 12 or 15 hours; that of " reconstitution for about 35 to 40 hours; 

 in winter the processes extend through about 10 hours more." 



* Ber. Naturf. Gesellsch. zu Freiburg, i. (1886). See Ann. and Mag. Nat. 

 Hist., xviii. (1886) pp. 164-5. 



t Comptes Rendus, ciii. (1886) pp. 482-4. 



