NOURISHING MEMBRANES 501 



to take yolk, and, having properly prepared it, to transfer it as a solution 

 into the blood. The cells are very large, and the nucleus lies in the prox- 

 imal end. The distal end shows masses of yolk which are in process of 

 food elaboration. 



The early stages of a teleost fish embryo show a proximal layer of 

 tissue which lies on the yolk and is probably used at this early period 

 to secure the nourishment from it. The layer is evidently cytoplasmic, 

 but it shows no cell boundaries, and is therefore syncytial (Fig. 470). 

 It contains enormous nuclei of a peculiar shape and chromatin pattern. 

 These nuclei are known as the paraUastic nuclei, and they multiply by 

 amitosis. Later they are done away with, and another form of nutritive 

 tissue is substituted. 



Technic. The nourishing tissues are easily cut in paraffin and should 

 be studied by individual sections fixed and treated for the best cytological 

 results. In some few cases it is desirable to understand the larger his- 

 tological relations, and for this purpose bulk-stained material should 

 be cut in celloidin. Sometimes serial sections of particular regions are 

 necessary, and bulk-stained material, cut in medium or soft paraffin, will 

 give the best results here. 



LITERATURE 



BRINKMANN. "Histologie, Histogenese, und Bedutung der Mucosa uteri einiger vivi- 

 paren Haie und Rochen," Mitt. Zool. Stat. zu Neapel, Band XVI, 1903. 



BROUHA. "Les phenomenes histologique de la Secretion lactee," Anat. Am., Band 

 XXVII, p. 464 (and later in Arch, de Biol.). 



STRAHL UND HAPPE. "Neue Beitrage zur Kenntnis von Affenplacenten," Anat. Am., 

 Vol. XXIV, 1904, S. 454- 



WILSON, H. V. "The Embryology of the Sea-bass, Serranus" Bull, of the U. S. F. C., 

 1893. 



