MUSEUM OF COMPAKATIVE ZOOLOGY. 253 



the canals are doubtless due to peculiar structural conditions of the fresh yolk, 

 though it is doubtful if they are ideiitical. 



Balbiani ('73, p. 77, Figs. 40, 79, 80) has seen a stellate arrangement of the 

 protoplasm about the nucleus as a centre in the blastoderm cells of Epeira in a 

 fresh condition. ■ '" 



Of interest in this connection are also the stellate differentiations in the pro- 

 toplasm of certain Ilhizopods. iv*s ~ : ."y -r 



' Grenacher ('69, p. 292, Taf. XXIV.-Fig. 1. d) describes for Acanthocystis 

 viridis an irregular central space filled with an apparently watery fluid, and 

 located in the centre of this a minute, pale corpuscle, from which radiate on all 

 sides numerous likewise' pale, fine -filaments, which fully agree with the axial 

 filaments of thia psteudopodia. A dii^ect continuation into the pseudopodia was 

 not- observed. . .--^ •'^' ' 



*.?-GifeBEFF ' ('7l, p. 6) confirms Grenacher's observation for A. viridis and other 

 species, as also for Actinophrys Eichhornii, and finds the rays to be continu-* 

 ati'ons of the fixiad' filaments 6f the pseudopodia. " - ■'■■^ !•■;.-- '/'"":(':• 



i SoifbL^^' ('74^' pp. 380-3S2, Taf. XXVI. Fig. 1) has-also observed a siihilWr 

 stru^cture in the case of Kaphidiophrys pallida, and established beyond doubt that 

 it is not with a siliceous skeleton that one has to do. Schulze's experiments^- 

 however, also show conclusively, if proof were at all needed, that the structure 

 in question can have nothing in common with molecular asters, which are not 

 destroyed, like the radial structures in Rhizopods, by acetic acid. 



b. Quiescent Nuclei. 



Many exceptions to the idea that the nucleus is a homogeneous compact 

 body have been recorded by the earlier embryologists and histologists, but it is 

 only within a comparatively short time that general assent has been given 

 to the belief that it is often an extremely complicated structure. 



Owing to their size, the nuclei of egg-cells have been much studied. In cer- 

 tain animals, especially the lower vertebrates, they have attracted attention 

 from the great number, and often the peculiar arrangement, of their nucleoli ; 

 as, for example, in the case of Alytes and several fishes studied by Vogt ('42, 

 pp. 1, 4, 15, Taf. I. Figs. 1, 2), in Cyprinus auratus according to Meckel von 

 Hemsbach ('52, p. 421, Taf. XV. Fig. 1), in turtles as described by L. Agassiz 

 ('57, pp. 475-479, PI. VIII., IX.), and in Rana as more recently investigated 

 by 0. Hertwig ('77, p. 36, Taf. IV. Fig. 1). 



The following authors, especially, have made interesting contributions to our 

 knowledge of the structure of the nuclei of eggs not in process of division. 



According to Eimer ('72«, pp. 216-220), the germinative vesicle in reptilian 

 eggs is of an exceedingly complex nature. The nucleoli are subject to the law 

 ot concentric arrangement which the author has elsewhere pointed out for the 

 nuclei of other cells. This arrangement reaches a cubnination in such stages 

 as are represented by him in Taf. XII. Fig. 18. The germinative dots are also 



