398 SUMMARY OF CURRENT RESEARCHES RELATING TO 



for staining, hssmatoxylin, picrocarmine, iodine, cliloride of gold, and 

 nitrate of silver are respectively recommended. Under the heading 

 Morphology is given a general sketch of the range of shape, size, 

 colour, consistency, and character of the surface in the group. Under 

 Anatomy is given an account of the different parts of the canal 

 system of sponges, and their chief modifications. The four types 

 under which the leading modifications of this system are arranged by 

 the author in a previous work are adopted here also. 



Protozoa. 



Nucleus and Nuclear Division in Protozoa.* — A. Gruber passes 

 in review the different groups of the Protozoa ; commencing with the 

 Ehizopoda, he points out that, though their nuclei differ considerably, 

 they are all referable to the type of the so-called vesicular nucleus. 

 There is a more or less distinct nuclear membrane, and a clear and 

 apparently homogeneous nuclear substance in which are deposited one 

 or more nuclear corpuscles. Such nuclei are to be found in the lowest 

 myxomycetoid plasmodia, and Biitschli is probably right in regarding 

 this form of nucleus as the primitive one ; previous to this, however, 

 there was, in all probability, a stage in which small granules of 

 nuclear substance were scattered through the whole of the protoplasm, 

 and these were only later collected into a proper nucleus. As a fact, 

 there are organisms which exhibit such characters ; as, for example, 

 some of the forms described by Maupas, the very low TrichospJicerium 

 sieboldi (Pachymyxa hysirix), and, probably, the Pleurophrys gennensis 

 discovered by the author. In all these we find small spheres 

 which are strongly coloured by certain reagents scattered through 

 the body. Moreover, as Brandt was the first to show. Amoeba proteus 

 contains not only a definite nucleus, but also small granules of nuclear 

 substance. 



Amoeba verrucosa is cited as an example of a form which, though 

 it seems to have a very definite vesicular nucleus, is found on ex- 

 amination with higher magnifying powers (e.g. Hartnack Oc. 3, 

 Obj. 12 Imm.) to have its nuclear corpuscles made up of smaller 

 spherules. When stained, these bodies gradually become less dis- 

 tinctly visible ; there appear in the substance of the nucleus excessively 

 fine granules, so fine as to have the appearance of a red dust ; these 

 would seem to be true chromatin particles, which may become united 

 into fine filaments ; they form lines arranged radially around the 

 nucleolus. They are best seen in specimens that have been treated 

 with absolute alcohol or picrocarmine. Although, therefore, there is 

 a nuclear network in Amoeba verrucosa it is very incomplete, and, as 

 observation has shown, takes no part in the division of the nucleus. 

 Multinucleolar nuclei are derived from the uninucleolar by repeated 

 division of the nucleolus. 



The division of the vesicular nucleus is effected by constriction or 

 by cleavage. In the former case, the chromatic substance is first 

 diffused through the whole nucleus ; in the latter ease the nucleolus 



* Zeitschr. f. Wiss. Zool., xl. (1884) pp. 121-53 (2 pis.). 



