140 SIDNEY F. HARMER. 



part of the cavity of the erabrvophore, and in one or two cases 

 it was found in the vestibule. 



The series of developmental stages grouped under the head- 

 ing of stage E is really a very long one ; and there are great 

 differences between ovicells at the two ends of the series. 

 This difference is marked in the measurements of all the parts 

 of the ovicell. 



In the early part of stage E the embryo remains for some 

 time in the position in which it was found in the preceding 

 stage, and its size does not at first materially increase. It is 

 now more or less spherical, and has a diameter of about 20 — 

 25 fx. Later in stage E the follicle becomes continuous with 

 the cavity of the embryophore. The embryo now begins to 

 elongate in the direction of the main axis of the ovicell, and 

 soon reaches a length of 40 — 50 ju, its transverse diameter 

 being at first small. With the increase of this diameter it 

 becomes ovoid, and then rapidly increases in size. Measure- 

 ments of the embryo fairly late in stage E amounted to 80 ft 

 for the major axis, and 50 ju for the miuor axis of the same 

 embryo. The oldest ovicell which I have found in this stage 

 had a pear-shaped embryo 135 fx long, with its narrow end 

 situated proximally. The ovicell had reached a considerable 

 size, its greatest transverse diameter, as measured in a series 

 of horizontal sections, being 1-25 mm. (= 1250 ju). The 

 cavity of the embryophore was spacious, and was cylindrical 

 for about its proximal half, the distal end dilating into the 

 form of a trefoil consisting of three lobes, the middle lobe 

 being connected with the vestibule. 



In most of the later ovicells studied in this stage the cavity 

 of the embryophore was either cylindrical (as in fig. 22), or was 

 somewhat dilated distally without being distinctly lobed. Be- 

 ginning this stage with a length ^ of about 150 fx, the embryo- 

 phore may reach a length of 500 /x by the end of this stage ; 

 and after the establishment of its cavity, its transverse diameter 

 may become as much as 450 ju at its distal end. 



^ This measurement is taken between the points C and B in the figures on 

 Plate 9. 



