206 SUMMARY OF CURRENT RESEARCHES RELATING TO 



considering it, on account of its having two nuclei, to be a new species, 

 assigns to it the name iV. duplex. This species undergoes encystation 

 occasionally, like the other Nuclearice, and during the process Maggi 

 saw the two nuclei increase by fission to four. Then followed the 

 division of the envelope of the cyst, in such a way that one of the por- 

 tions into which it divided enclosed the old nuclei, and the other the 

 newly-formed nuclei. This bi-nucleate Nudearia the author believes 

 himself justified in regarding as exhibiting a most important phylo- 

 genetic step towards the bi-nucleate condition shown by the fertilized 

 ovum in the simultaneous occurrence of a male and a female nucleus, 

 and finds the explanation of this doubly-nucleate developmental stage 

 of the Metazoan ovum to lie in the existence of a phylogenetic 

 bi-nucleate Protozoan predecessor of the character here described. 



G. Cattaneo,* after a short historical survey of the investigations 

 which have been made among the Heliozoa, describes his observations 

 on Acantliocystis flava Greef, made on a single specimen in the course 

 of two mornings. As might have been expected, he has but few 

 facts to show, although the conclusions which he strives to draw 

 from them are none the less far-reaching. He cannot regard the 

 external, vitreous, colourless protoplasmic zone of A. Jlava, which 

 has been described as ectosarc by various authors, as such, but con- 

 siders it to be what he terms mesoplasm. The reasons for this opinion 

 are that it contains the contractile vacuole, and sends out the fine 

 pseudopodia which serve only as organs of prehension, these being the 

 characters of the mesoplasm, as elaborated by Maggi in the case of 

 Podostoma, &c. The ectoplasm proper of the present form, Acantlio- 

 cystis, is said to be developed into the silicious skeleton, which cannot 

 be regarded as a product of excretion of what is usually called meso- 

 plasm. Tho author finds a confirmation of this view in the relations 

 of the parts of the so-called chlamydophorous Heliozoa, in which the 

 ectoplasm proj)er is still to be found in the condition of an external 

 envelope, while further on in the developmental history of Arcella 

 vulgaris, as described by him, he finds that the ectoplasm which is 

 present in the young stages developes later into the shell.j The 

 author, of course, extends this view as to the nature of the investing 

 skeleton to all the Heliozoa which have skeletons. 



Cattaneo also states that he has observed the following. The 

 simple central nucleus, said to possess a deeper brown coloration 

 than the investing entosarc, was divided by a constriction after its 

 nucleolus had become double. One half of the nucleus remained in 

 the centre, while the other wandered to the surface of the entoplasm. 

 Brown granules then became developed in numbers, and were finally 

 scattered through the entosarc ; they are regarded by the author as 

 spores. From this observation he believes it necessary to doubt the 

 occurrence of simple fission under any form in such highly-developed 



» Atti Soc. Ital. Sci. Nat,, xxil. (1880) p. 46 (1 pi.). Of. Zool. Jahresber. 

 Neapel for 1880, i. p. 155. 



t Professor O. Biitscbli remarks (Zool. Jaliresber. Neapel for 1880, i. p. 155) 

 of this observation, that it justifies an opinion expressed by himself in Zool. 

 Jabresber. Neapel for 1879, as to the probability of an origin of this kind for the 

 shell of Arcella. 



