86 RICHARD EVANS. 



developing ova surrounded by follicle cells derived from the ventral 

 wall of the ovary, and hanging freely in the hsemoccele. 

 Fig. 17 c. — This figure shows a portion of the oviduct in the section snc- 

 ceeding that illustrated in Fig. 17 a. Note the rudiment of the recep- 

 taculum ovorum {rec. o.) developed as a simple outgrowth from the 

 wall of the oviduct. 



Figs. 18 a, 18 i, 18 c, and 18 r/ ( X 170).— These figures represent four stages 

 in the growth of the ovarian ovum. 



Fig. 18 a. — This figure shows an ovum in which the cytoplasm possesses 

 a beautifully alveolar structure. The nucleus, placed near the centre 

 and circular in outline, is provided with a nucleolus which is alveolar 

 in character. 



Fig. 18 b. — This figure shows an ovum very similar in structure to the 

 one shown in the previous figure, but of greater dimensions in all its 

 parts. 



F'ig. 18 e. — This figure shows an ovum in which the cytoplasm is occupied 

 by a large number of globules which are almost uniform in size, and 

 are situated in the alveoli shown in Figs. 18 « and 18 6. 



Fig. 18 d. — This figure shows a transverse section of an almost fully 

 grown ovarian ovum. The globules shown in the foregoing figure 

 have fused to form compound systems. The nucleus has wandered 

 from the centre towards the periphery, and consequently has become 

 irregular in outline. Note also the disposition of the yolk-bodies with 

 regard to the nucleus. 



Figs. 19 a, 19 b, and 19 c ( X 170). — These figures represent sections of an 

 embryo slightly older than that sections of which are illustrated in Figs. 16 a, 

 b, and c. 



Fig. 19 a. — This figure shows a transverse section through the third pair 

 of somites from the posterior end {som."'''). The vasa deferentia open 

 to the exterior by a short common duct, a condition which is per- 

 manent in the female {vas. de/.). 



Fig. 19 I/. — This figure shows a cross-section of the left vas deferens 

 near its inner end, and a section through the funnel of the right vas 

 deferens. 



Fig. 19 c. — This figure shows a section through the developing testes, 

 showing the germinal nuclei filling the internal cavity, and surrounded 

 by an epithelial layer. Both testes are fused to the ventral wall of the 

 pericardium, and are situated close together, much in the same way 

 as the developing ovaries are in Fig. 16 c. 



Figs. 20 a and 20 i (X 170). — These figures represent sections of a male 

 cmbrvo of the same, age as the one shown in Fig. 5. 



