So PRIMITIVE FORMS OF LIFE 



to produce seven, eight, or nine 1 at a time. To cite a more 

 extreme instance, if the fertilized egg of the sea-urchin is 

 placed in water deprived of calcium, as in Herbst's experiment, 

 the first thirty-two blastomeres can separate and develop in- 

 dependently, and produce the beginnings of as many as thirty- two 

 embryos. Such a division is produced naturally in the embryo of 

 certain minute four-winged flies, akin to the wasps, and which 

 might indeed be considered as lilliputian wasps. The larvae 

 of these insects, minute in size but already highly organized, 

 develop either within other larvae imprisoned in galls, the larvae of 

 certain mosquitoes, the Cecidomyia, or more frequently in very 

 small common caterpillars, like those of the moths of the genus 

 Hyponomeutia which live on the spindle-wood. The parasitical 

 caterpillars always contain a multitude of larvae. As many as 

 three thousand have been counted, and for a long time naturalists 

 were puzzled as to why there was no intermediate condition be- 

 tween the presence of vast numbers of parasites and complete 

 immunity, since the fertilized fly itself contains not more than a 

 hundred eggs. The problem was solved by Marchal. 2 The em- 

 bryos of the majority of insects are enclosed in a sac, the amnion, 

 derived like them from a cellular membrane, the blastoderm, 

 formed by the division of the nucleus of the egg. In the case of 

 the minute parasites in question, the egg commences by 

 dividing into two halves, one of which develops into the amnion 

 and the other, generally, into a single embryo. In certain 

 species, however, the elements that are destined to form the 

 embryo separate and develop independently, so that ten, 3 

 two hundred, 4 or even three thousand larvae, 5 varying with the 

 species, may be born from a single egg. The blastomeres, in 

 this case, retain their likeness throughout a large number of 

 fissions. 



In those eggs containing reserve substances what happens 

 is quite different ; this has led to embryogenetic conceptions 

 that are entirely erroneous, because the facts were generalized 

 without reference to their causes. 



1 Von Jehring had in 18S5-6 already concluded from this the disjunction 

 of the egg, a fact that was later confirmed by Miguel Fernandez in 1909 (XXXIII) . 



2 XXXIV. 



3 Polygnotus minntus, the parasite of the Cecidomyidae (Marchal). 



4 Encyrtus (Ascidiaspis) fusicollis, the parasite of the caterpillar 

 of Hyponomeutia of the spindle-wood (Marchal). 



5 Litomastix, the parasite of the caterpillars of the nocturnal butterflies 

 of the genus Plusia (Silvestris). 



