324 DEVELOPMENT OF ASCIDIANS 



(1931), Ries (1939), and Tung et al. (1941) described granules 

 which are not stained by the Janus green. They are osmophihc 

 and are brought by centrifugation to the centripetal pole. They 

 are also rich in yellow pigment from which derives the typical 

 "yellow crescent" described by Conklin. Such granules are sup- 

 posed to be mitochondria because they behave like them when 

 treated with ordinary lipidic solvents or with osmic acid. On the 

 other hand, we have described rodlike mitochondria, which take 

 the coloration with the Janus green and which gather, by cen- 

 trifugation, above the equator of the egg, between the hyaline 

 cap and the pigmented zone. Secondly, we have also noticed, 

 especially at the time of their segmentation, that the non-muscle- 

 forming blastomeres of the embryo possess, although in small 

 number, typical mitochondria. 



Enzymes of the Ascidian Mitochondria 



The present knowledge on the quality, quantity, and localiza- 

 tion of the enzymes in the mitochondria is generally very poor, 

 because only a few histochemical techniques are at our disposal. 

 Ries (1937) was the first to indicate the presence and localiza- 

 tion in the cells of the developing ascidian egg of "indophenoloxi- 

 dase," "benzidinperoxidase," and "oxidoreductase." These en- 

 zymes were segregated in the cells of the muscle line. Reverberi 

 and Pitotti ( 1939 ) confirmed these points and showed that the 

 pattern of the enzymatic distribution is very different in the un- 

 fertilized and in the fertilized egg. 



Ries supposed that these enzymes are not localized in the mito- 

 chondria but in the plasm. He attributed a paramount importance 

 to them in relation to the differentiation of the musculature, and 

 he stated that only when the plasm containing these enzymes 

 is displaced by centrifugation, larvae arise which are very defi- 

 cient in musculature. The displacement of the mitochondria is, 

 according to Ries, of no consequence to morphogenesis. 



Our recent research has shown that the indophenoloxidase of 

 Ries is inhibited by sodium azide; thus, it must be identified as a 

 cytochrome oxidase; also it is localized not in the plasm but in the 

 mitochondria. In fact, the mitochondrial zone of the centrifuged 



