290 ^^- KISHIXOUYE. 



an unpaired cavity in thi.s atage. In the abdomen the growth of the 

 mesodermic .somites, except thîit of the first abdominal segment, is 

 enormous, extending rapidly towards the dorsal median line. Thus 

 in the abdomen, the dorsal portion of the cœlomic cavities develops 

 rapidly, while their ventral portion as well as the portion Avhich enters 

 into the appendage remains only slightly developed. In the céphalo- 

 thorax, on the contrary, the portion of the cœlomic cavities which 

 enters into the appendage develops rapidly, while their ventral and 

 dorsal portions remain undeveloped. 



The reversion of the embryo now begins, and when the process 

 advances a little, the two nerve cords and the appendages of both 

 sides of the ^'entral j^late, «n* the two lateral divisions of the germinal 

 band, begin to separate from each other. This lateral extension of the 

 ventral plate, together with the rapid growth (jf the dorsal portion of 

 the mesodermic somites in the abdomen, causes the dorsum of the 

 embryo to elongate longitudinally. At this stage the mesoderm of 

 the céphalothorax shows no noteworthy changes. The C(L'lomic 

 cavities of the cephalic lolje develop anteriorly, or towards the dorsal 

 region (Tigs. 7, 8). The first abdominal segment begins to de- 

 generate ; its mesodermic moieties and ganglia may however be seen 

 with some ditliculty. In the second to fifth abdominal segments the 

 mesodermic moieties develop greatly towards the dorsal median line, 

 so that they nearly meet each other at that line (Fig. 7). The 

 ectoderm covering these mesodermic somites is elevated a little, and 

 forms the s(j- called tergal portion of the abdominal segment. Locy* 

 illustrates his paper with a figure (PI. II. Fig. D) in which a pair of 

 terga may be seen before the second a1jd(jminal segment ; Ijut he gives 

 no description of them. I myself am unable to find them, lie says 



* Uu the Development of Agalena Dtevia. Bull. Mus. Comp. Zoul., vol. Xll. 1886. 



