332 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



1949; Lehmann, 1956; Weber, 1956) ; the recent investigation of Weber (1958) on 

 the submicroscopic organization and on the biochemical features of these eggs has 

 clearly shown that the differences related to the distribution of the classical plasm 

 can be attributed to the relative frequency of mitochondria, ultramicrosomes and 

 other active particles. This conclusion is also valid for moUuscan eggs, e.g. Ilyanassa 

 (Clement, 1956; Clement and Lehmann, 1956). Thereby, cleavage acquires a 

 definitely constructive value. 



This positive role of cleavage in the preliminary steps of morphochoresis is also 

 made plain by another, less known trend of research, an account to which will 

 now be given. 



In 1950, Kelly described in vivo metachromasia in Chaetopterus eggs that has 

 been stained with toluidine blue. This author believed this metachromasia was 

 due to the presence of heparinlike substances, and insisted that this treatment 

 did not in anyway alter the development. 



Independently, it was found that when staining rat eggs (ist to 5th day) with 

 toluidine blue — lo"^, there is a striking appearance of metachromatic granules, 

 which show distinct differences at various stages (Dalcq, 195 1). Extended to 

 other mammalian eggs (mouse, rabbit, guinea pig), this procedure has proved 

 a most useful method for revealing various cytochemical processes. Special 

 groups of chromotrope granules, which at first were thought to be mitochondria, 

 display metachromasy, apparently because they are activated by nuclear emis- 

 sions. Their distribution corresponds to some organization of the cytoplasm 

 (Fig. 20, 21; Dalcq, 1954c; Izquierdo, 1955). They are more abundant in the 

 ventral half of the egg, and their number and importance increase during the 

 first steps of cleavage (with an apparent reduction during active mitosis). These 

 metachromatic granulations were shown to contain mucopolysaccharides (Fig. 2 1 ; 

 Mulnard and Dalcq, 1955) and were shown to synthetise acid phosphatase in 

 increasing quantities (Mulnard, 1955). In the hyaloplasm lying between these 

 granules an excess of acetalphosphatides (true plasmalogene) could be demon- 

 strated (Dalcq, 1956a). More recently, it was shown by using brillant cresyl blue 

 combined with Janus green B, and recourse to centrifugation, that the chromo- 

 trope metachromatic granules are distinct from the mitochondria. (Dalcq and De 

 Greef, 1958). 



Since 1955, a similar analysis has been performed on various invertebrate eggs, 

 with the advantage that some basic metachromatic dyes behave as truly vital stains 

 in most species^ So far the enquiry has now concerned the eggs of sea urchins 

 (Pasteels, 1955a, 1958; Mulnard, 1958; Vercauteren, 1958; Brice, 1959), of two 

 bivalve mollusks, the clam Barnea and the oyster Gryphaea (Pasteels, 1955a; 

 Pasteels and Mulnard, 1957), the worm Chaetopterus (Mulnard, 1958) and finally 

 ascidians (Dalcq, 1957c, 1959). Admitting some restrictions for the last group, in 

 which cytochemical analysis has to be continued, the chromotrope and meta- 

 chromatic equipment of these eggs show rather uniform features. 



The prerequisite for good vital staining is that the eggs are exposed for a few minutes 

 to the penetration of the dye — the less toxic one being brilliant cresyl blue (3.10"'*) — and 



Marthasterias glacialis excepted (Brice, 1959a) 



