OF OECANTHUS AND TELEAS 



233 



4. Micropylar cap — produced by the follicular epithelium at the anterior end of the 



ovariole — possesses a very complicated structure. 



5. Vitelline membrane — secreted by protoplasm of egg — structure similar to zona 



racliata of other animals. 

 From the above it is seen that the membranes are derived from three different sources — 

 the egg itself, the follicular epithelium, and the vaginal mucous glands. The mucous 

 coating is very thin when dry and is only to be detected on eggs treated with caustic soda 

 or water ; it is most abundant about the micrcmylar cap, frequently filling the spaces 

 between the papillae. 



The outer chorion is a dense, tough, homogeneous membrane marked with a series .of 

 parallel and cross surface cracks (PI. 20, fig. 11, and Fig. 12, below) which are arranged with 

 an extreme irregularity quite characteristic. The different systems of surface cracks cover 

 limited areas and incline at various angles to each other. This arrangement of parallel and 

 cross lines at varying angles of intersection reminds one of a city map in which the rectangular 

 system of streets for each addition was laid out regardless of the direction in neighboring 

 parts. The surface cracks, or grooves, in this layer vary in their depth, frequently extend- 

 ing nearly through the membrane. In the figure they should be represented by two parallel 

 lines, since they are open spaces bordered on each side by the sharp edges of the mem- 

 brane. The areas are sometimes perfect squares but usually when rectangular they are 

 several times as long as they are broad. This layer tears with a sinuous outline across 

 the cracks and solid membrane indifferently. Until near the time of the revolution of the 

 embryo in the egg, this membrane is intact, and when the egg is ruptured it determines the 

 course of the rupture of the other membranes. Just before revolution the outer layer 

 is burst by the swelling of the egg and exposes the transparent inner layer. The relation 

 of the cracks to the membrane, and of the membranes to each other and to the egg, is 

 best shown in section. (PI. 20, fig. 21.) This layer is deeply stained in safranine, 

 haematoxylin and picro-carmine, but remains unstained in other dyes. Its thickness varies 



from 3.5 fi to 4 a. On treatment 

 - : u\ w with caustic soda it swells rapidly. 



At first small sac-like elevations 

 appear over the surface of the 

 egg ; these gradually coalescing 

 form a loose sac about the lat- 

 ter and remain united with it 

 at the micropylar end where 

 all the layers are more or less 

 fused. During this swelling pro- 

 cess the cracks disappear, the 

 „ , v , , ,- ■.••.!• micropylar papillae enlarge, be- 



Surface view of the egg membranes and the serosa, from a chromic acid, glycerine 1- -^ r I c 



preparation, x 400 . come transparent, and show a 



distinctly marked, central, curved lumen. If the action of the reagent is continued the 

 inner chorion is atiVted in the manner described for the outer chorion, also coining away 

 from the egg as a loose sac. Frequently one sees in this inner sac a mass of granular 

 matter. The vitelline membrane does not swell in the alkali, but when brought in con- 



MEMOIRS BOST. SOC. NAT. HIST. VOL. III. 



30 



