description of the ovum and the processes of division 

 inside it up to the formation of the embryo," Schmidt 

 wrote, "was given so completely by van Beneden and 

 Windischmann that I cannot add anything to it" (p. 278). 



The subject of Nordmann's above mentioned work on the 

 development of the gastropodan molluscs was the nudibranchiate 

 mollusc Tergipes Edwardsii . The description of the phenomena 

 of its embryonic development constitutes part of the extensive 

 monograph, 19 beginning with the presentation of anatomical 

 data. Nordmann described in detail the development of the 

 ovum in the ovary (5 28 - 31), characterized the yolk 

 elements of the ovum (§ 32) , the structure of the egg 

 ready for oviposition (5 33) and its membranes (5 34) . The 

 process of division {§ 39) of the ovum of Tergipes was 

 described by Nordmann as the following: the first fissure 

 of division can take place in different directions and 

 divide the ovum either into equal, or into very unequal 

 parts. The fissure dividing the ovum into four globules 

 of division takes place at right angles to the first 

 fissure, after which the ovum is divided into eight globules, 

 and so on. The generally uneven character of division is 

 noted in the following expression. "Although the tendency 

 to even progressive division cannot be disputed, it also 

 shows that the yolk, especially up to its acquisition of 

 the mulberry form, appears to divide very unevenly" (p. 573) 

 (Figure 38, a-g) . Nordmann noted especially that the fissures 

 cut all the mass of the yolk, i.e. that the division was 

 complete. 



All the course of development of Tergipes Nordmann sum- 

 marized in the following statements: 



19. Nordmann, "Versuch einer Natur- und Entwickelungsgeschichte 

 des Tergipes E 'dwards ii , " MEM . , pres . a l'Acad. Sc. 

 St.-Petersb. par divers savants, 4 (1845) , pp. 495 - 602. 

 A brief translation of this work in French was published 

 by K. Fogt ("Essai d'une monographie du Tergipes Edwardsii," 

 ANN. SC. NAT., 3, ser. Zool., 5 (1846), pp. 109 - 160). 



534 



