CF OECANTHUS AND TELEAS. 257 



In the nuclei of the epithelial cells from the follicles of the ovariole of Oecanthus (pi. 21, 

 figs. 43-50 ; pi. 23, figs. 17, 18, 20) the nucleoli vary greatly in shape and number. There 

 maybe a single spherical or dumb-bell shaped nucleolus, or the latter may assume the con- 

 dition of a thick rod. It may be lacking entirely or may consist of a central body with few 

 or many, small or large, radiating threads. Whenever more than one nucleolar body is 

 present the nucleus is more or less elongated and usually shows some indications of 

 approaching division. The occurence of anything like a symmetrical nuclear spindle is 

 rare in such cells. The arrangement of the nuclear substance in the form of filaments is 

 exceedingly various, but out of all the material studied, I have not been able to trace any 

 definite cycle of conditions through which the nuclear filaments pass during the division 

 of the nucleus, such as has been described by Flemming, Strasburger and others for both 

 animal and vegetable cells. However, many of the stages which I have observed corre- 

 spond to those given in tbeir schemes of cell division. The most common form of filament 

 as a short, tortuous, refractive thread, which is woven into a filamentous mass so as to be 

 traceable for only short distances in any direction. This thread may appear moniliform 

 or continuous. 



The filamentous structures of the germinative vesicle at various stages in the growth of 

 the ovum, although characteristic, do not differ in essential particulars from similar struc- 

 tures in tissue cells. In the follicular epithelium the threads are frequently arranged in 

 loops at the periphery of the nucleus while at their central ends they are connected with 

 the larger masses of nuclear substance, — nucleoli, — from which they may be said to spring. 



The physical and chemical conditions of the yolk nuclei differ considerably from those 

 of the nuclei of tissue cells, as is at once apparent upon treatment with reagents. The 

 yolk nuclei are larger than any others in the embryo and are less numerous. They multi- 

 ply much faster, but their descendants usually differ greatly from them, as for example 

 when a single yolk nucleus by rapid prolifex*ation gives rise to many mesodermic nuclei. 

 When treated with osmic acid and Beale's carmine the nuclear matter separates into two 

 distinct parts, the nuclear fluid and the nuclear substance. The latter is usually contracted 

 into an irregular mass near the centre of the nucleus, but the compactness of this central 

 mass depends entirely upon the kind and strength of the reagent used. If the reagent is 

 too strong, the nuclear substance will be entirely torn away from the membrane and be 

 contracted into an apparently homogeneous mass, but if a weak solution is used many of 

 the filaments will still retain their connection with the nuclear membrane, whereas the cen- 

 tral mass will appear finely granular with here and there filaments stretching out toward the 

 periphery of the nucleus. The spaces between these radiating filaments are filled by a 

 feebly stainable substance, the nuclear fluid. The nucleoli do not stain so deeply as the 

 filaments, and the membrane stains scarcely at all. The size and condition of the nuclear 

 filaments vary greatly in different nuclei and, consequently, one infers in different stages 

 of the growth of the same nucleus. The nucleolus is not always present, but when it is, the 

 nuclear filaments are usually seen to be more closely intertwined in its vicinity than in 

 other parts of the nucleus. The nucleolus may appear filamentous or homogeneous in its 

 structure ; in the Litter case the nuclear filaments have no connection with it. Sometimes 

 the nucleolus may be enveloped in a clear mass of protoplasm in which no filaments are to 

 be detected. Such nucleoli are probably the homologues of the polar corpuscles which 



MEMOIRS HOST. SOC. NAT. HIST. VOL. III. 33 



