42 W. BALDWIN SPENOEE. 



The dorsal wall is more definite in shape than in the early 

 stages_, being very thick in the central line, and thinning out 

 rapidly towards the sides. It is, as before, formed in reality 

 of a syncytium broken up into irregular masses of protoplasm, 

 each of which contains many small nuclei {Sy.). 



The lumen is continued laterally into pouch-like diverticula 

 {L. S. 0.), more prominent and numerous than in the earlier 

 stages ; and these are surrounded by a mass composed of proto- 

 plasm and nuclei, the outlines of cells being visible in parts. 



The upper wall close to the main lumen is distinctly marked, 

 and evidently a continuation of the dorsal wall of the ovary. 

 The nuclei in the mass around the diverticula are of various 

 sizes, and it is evident that in this portion the formation of 

 cells is proceeding. 



Compared with the earlier stages (fig. 44) the ovary [has 

 both been compressed dorso-ventrally, and has grown out 

 laterally. The cells forming the original " crest " have become 

 more or less separated from one another, modified as will be 

 described, and spread out over the whole external surface. In 

 the earlier stage the dorsal walls of the diverticula were 

 formed in part by the lateral portions of the syncytial mass 

 which formed the dorsal wall of the ovary. In the fully 

 developed stage it appears as if rapid division of the nuclei 

 takes place in the latter part, which, again, is continuous with 

 an ill-defiued mass of protoplasm present on either side, into 

 which project a series of diverticula from the main lumen of 

 the ovary. 



The original dorsal wall may thus be regarded as having 

 become divided into two parts : — (1) The central part, contain- 

 ing numberless nuclei, which are here undergoing division ; 

 and (2) the lateral portions, into which the nuclei from the 

 former pass, and in which tliey appear to increase in size, and 

 to be surrounded by protoplasm, with the resultant formation 

 of definite cells. 



{b) Oviducts. — These diflfer only slightly from those 

 described by Leuckart^ in P. tsenioides, and more especially 

 ' Loc. cit., p. 85, Taf. xi, figs. 17—19. 



