154 BIOLOGICAL LECTURES. 



all segregations of formed substance within the nucleus, not 

 including the chromatin, linin, caryolymph (and the problemat- 

 ical lanthanin granules?), probably should be regarded as true 

 nucleoli. Or, in other words, our criterion of nucleoli probably 

 should not be based as much upon chemical as upon morpho- 

 logical facts : the criterion should be rather its mode of forma- 

 tion and deposition than its chemical nature, for there is reason 

 to believe, as I think the facts here presented will show, that 

 the nucleolus is a substance formed under the action of nutri- 

 tive metabolism, and hence that its chemical nature may vary 

 in different cells, and at different stages of. the same cell, just 

 as the kind of nutrition varies in different cells and at different 

 stages. In estimating the valence of a nucleolar structure, its 

 morphology must be considered as well as its chemistry, and 

 not its chemical nature alone. 



The present lecture gives a short review of a few of the 

 observations made by me upon different cells, while the detailed 

 observations, accompanied by figures and literature reviews, are 

 contained in two papers, one (not yet published) in the Journal 

 of Morphology, and the other in Spengel's Zoologische Jahrbiicher 

 for 1 898 ; the former paper, dealing mainly with the true nucleo- 

 lus, was completed in February, 1897; and the second, on the 

 spermatogenesis of Euchistus (Pentatoma), in April, 1898. The 

 objects studied in the former paper were the germinal vesicles 

 of nudibranch Mollusca (Montagua, Doto), of Nemerteans (Tet- 

 rastemma, Amphiporus, Zygonemertes, Lineus), of the polychaete 

 annelid Polydora, of the leech Piscicola, and of the siphonophore 

 Rodalia; further, nuclei of two Gregarines, and of various 

 ganglion, gland, muscle, and blood cells of the forms mentioned 

 above, and the hypodermis of the larva of Carpocapsa. 



I. THE TRUE NUCLEOLUS. 



With Delafield's or Ehrlich's haematoxylin, followed by eosin, 

 the nucleolus stains red ; while with the Ehrlich-Biondi-Heiden- 

 hain mixture as usually employed it is stained red or orange. 



i. Number and Size. The usual number is about 1-5 to a 

 nucleus, but in many cells a much larger number is present. 



