AMERICAN NATURALIST 



V..].. XXX. 



ON HEREDITY AND REJUVENATION. 



By Charles Sedgwick Minot. 



(Continued from page 9.) 



III. A Comparison of Larva and Embryo. 8 



It has long been known that animals develop according to 

 two types, appearing in their younger stages, either as larvae 

 or as embryos. The larvse lead a free life and must obtain their 

 own food. Embryos, on the contrary, do not lead a free life 

 and are nourished by the yolk accumulated in the parent 

 ovum. There is, of course, no absolute demarcation between 

 the two classes ; nevertheless, a general comparison between 

 them establishes several conclusions which throw valuable 

 light upon some recent biological hypothesis. 



First of all, it must be remarked that the larval develop- 

 ment is primitive, and that the embryonic development has 

 been evolved later. Geologists are able to present two princi- 

 pal supports for this assertion : 1. In the lower animals we 

 encounter only larvse, never embryos ; sponges, colenterates, 

 echinoderms and worms, all pass through the early stages of 



8 Bead before the Amer. Soc. of Morphologists, December, 1893. 



