No. I.] EMBRYOLOGY OF THE ISOPOD CRUSTACEA. 127 



Some of these cells are becoming muscle cells {imi) and will 

 eventually produce the longitudinal dorsal muscles of the 

 abdominal region, while others do not become thus trans- 

 formed, but retain their original character in much later stages. 

 Whether or not they become blood corpuscles I cannot cer- 

 tainly state, though from what I have seen in sections through 

 later stages I am inclined to believe that that is, in part at all 

 events, their fate. 



In the oldest embryos of CymotJioa which I possess the organs 

 are all fully formed, and there is no trace of yolk in its original 

 condition to be found. In slightly earlier stages the digestive 

 tract is complete, and there is still a certain amount of yolk 

 present in the thoracic region of the body, and within it vitello- 

 phags are to be seen, and there does not seem to be any possi- 

 bility that these cells enter into the formation of the digestive 

 tract ; in fact I have seen no indications that any of the vitello- 

 phags do so. In the latest embryos (Fig. 68) the spaces be- 

 tween the various organs are occupied by a granular mass {dy) 

 which resembles in appearance the granular disintegrated yolk 

 seen in the dorsal region of Fig. ^J {dy), and I believe this 

 matter is of the same nature and represents the final condition 

 of the yolk. It occupies the place of the blood plasma, and 

 has imbedded in it a certain number of amoeboid cells (vi), the 

 blood corpuscles, which are, there is every reason to believe, 

 persistent vitellophags. This result agrees perfectly with the 

 observations of Nusbaum on Mysis i^on), and I can confirm for 

 CymotJioa the statements contained in the last two paragraphs 

 of page 192 of his paper. 



Not all the vitellophag cells take part, however, in the forma- 

 tion of persistent tissues. Some appear to break down, being 

 enclosed within the liver lobes, and others seem to disintegrate 

 independently of the action of the liver, giving rise to particles 

 of chromatin such as may be seen in Fig. 6^ {Cr) scattered 

 among the cells at the surface of the yolk, and resembling the 

 chromatin nebulae, which have been described by various 

 students of Decapod embryology. So far as I have seen, how- 

 ever, such disintegrating cells are few in the Isopods, and are 

 to be found only in the latest stages of embryonic development. 



