ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 331 



Echinoderma. 



Cuvier's Organs in Holothuroids. * — Sig. A. Eusso has studied these 

 in Holothuria for shall and H. hellerl, where they arise as evaginations of 

 the cloacal wall directly under the opening of the respiratory trees. 

 The cavity of the diverticulum has its epithelium modified to form the 

 axial canal of the fully formed organ ; but sometimes, as in H. hellerl, 

 this quite disappears. The coelomic epithelium covering the external 

 surface becomes glandular. Eusso regards the organs as equivalent 

 to the interradial caeca of starfishes, and as functionally defensive. 



Development of Asterina gibbosa.t — Prof. E. W. MacBride dis- 

 cusses the points at issue between Mr. Seitaro Goto J and himself ou this 

 subject, and figures some new sections which he thinks confirm entirely 

 his own views. In the first place, Goto believes that the symmetry of 

 the larva and adult are identical, though this fact is rendered obscure by 

 the bending of the prseoral lobe to the right side. MacBride finds no 

 trace of this secondary bending, and believes that the slight and incon- 

 stant flexures which may occur, either to the right or the left, are due to 

 the action of preservatives only. He finds no correspondence between 

 the planes of symmetry of the larva and the adult. Further, his re- 

 newed observations fully confirm his former statements that the coelom 

 on each side of the larva is divided into an anterior and a posterior part 

 by a transverse septum, while Goto states that a posterior enterocoele 

 arises at the left side of the larva only. Again, Goto denies that the 

 structure described by MacBride as the right hydrocoele deserves this 

 name, for he believes that it arises from the left ccelomic sac. MacBride 

 holds that this is an error due to the fact that Goto did not observe the 

 earliest stages of the development of the structure. Finally, MacBride 

 is able to confirm his previous statement that the distal portions of the 

 radial perihsemal canals are coelomic in origin, as against Goto's asser- 

 tion that they are formed by the hollowing out of masses of mesenchyme. 



Connection between Blastomeres in Sea-Urchin Eggs.§ — Prof. J. 

 Aug. Hammar discusses the bearing of recent observations on his view 

 that there is a primary protoplasmic connection between the blastomeres 

 of segmenting eggs. The existence of such a connection is denied by 

 no one, but certain authorities have regarded it as being of membranous 

 nature. By a careful comparison of the statements of different observers, 

 the author shows that these all tend to confirm his view that it is truly 

 protoplasmic. Other authorities, however, such as Flemming, admit the 

 protoplasmic nature of the connection, but deny that it is primary. In 

 the investigation of this problem the author has studied the segmentation 

 of the egg in the sea-urchins Echinus miliar is and Ampliidetus cordatus. 

 He finds that in both cases the first segmentation furrow has two com- 

 ponents ; its outer and less important part is formed by an indimpling, its 

 more central part by a splitting of the protoplasm. This internal cleft 

 constitutes the first rudiment of the segmentation cavity, and at the close 

 of the first segmentation is traversed by a slight protoplasmic band, which 

 connects the two blastomeres. These are also connected together by a 



* Monit. Zool. Ital., x. (1899) pp. 133-41 (1 pi.). See Zool. Centralbl., vii. 

 (1900) pp. 140-1. 



t Zool. Anzeig., xxiii. (1900) pp. 98-104 (3 figs.). Cf. this Journal, 1896, p. 421. 

 % Journ. Imp. Coll. Sci. Tokio, xii. Cf. this Journal, 1S99, p. 40. 

 § Arch. Mikr. Anat., lv. (1900) pp. 313-36 (1 pi.). 



