of the Moscow Society of Nature Investigators, Gimmerthal, 

 several times reported from Riga about his observations on 

 the metamorphosis of flies (genus Tachina) and butterflies 

 (Naotua ooculatd) .40 



Another native of Riga, V. Sodovskii, later published a 

 fairly extensive article about the development of butterflies, 

 with comparative data on the structure of eggs of caterpillars 

 and butterflies and of different scaly-winged insects. In 

 the embryological part of this article Sodovskii discussed 

 especially the process of covering the yolk with the blasto- 

 derm, and the development of two embryonic membranes — the 

 amnion and the chorion. 41 



Pander's significant contributions begin with his 

 definition of the meaning of the blastoderm. He was the 

 first to define that each of the layers or sheets of the 

 blastoderm (he frequently called them membranes) represent 

 the rudiment of a certain system of organs of the developing 

 chick. Therefore Pander must be considered the establisher 

 of studies about the embryonic membranes. The Latin names 

 which Pander gave the membranes — membrana pituitosa, 

 vasculosa, serosa — remained in embryology for a long time; 

 eventually the terms were replaced by the current non- 

 expressive Greekterms — endoderm, mesoderm, and ectoderm — 

 which do not allow such easy and clear translation. 



Next, Pander discovered the primary folds which constitute 

 the first signs of embryonic formation. In fact, Pander did 

 not succeed in connecting these with the formation of the 

 spinal cord, but his wrong interpretation played its positive 

 role. Pander's observations allowed Baer to give the true 

 interpretation. They were sufficiently accurate to eliminate 

 confusion in the description of features, and only the 

 interpretation happened to be wrong. Baer, on another 

 occasion, sympathetically cited Bacon, who said that a mistake 

 leads to the truth more quickly than to confusion. 



40. "Metamorphose des insectes. Observations extraites des 

 lettres de M. Gimmerthal a Riga," BULL. SOC. NAT. 

 Moscow, I (1829), pp. 136-141. 



41. W. Sodofsy, "Uber die Metamorphose des Schmetterlings , " 

 ARBEITEN DES NATURFORSCHENDEN VEREINS ZU RIGA, 



I (1847) , pp. 61-82. 



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