MICROSCOPICAL STUDIES. 73 



progression adopted by the two. The Lobster larva moves largely 

 by a jerky movement or flapping, produced by the muscular con- 

 traction of the powerful abdomen : the Phyllosome on the other hand 

 swims entirely by the paddling action of the thoracic legs. In the 

 one case, the animal chooses a mode of progression requiring a well 

 developed and muscular abdomen — in the other, Phyllosoma elects a 

 method that dispenses with the need for such a strong tail, hence the 

 non-development of that during such period when indeed it would be 

 an encumbrance and a danger. Then* as to the change in form of 

 the rest of the body — such is probably the outcome of the greater 

 pelagic habit of the Phyllosome. The latter has a much longer 

 surface-swimming larval life (so far as my observations go) than 

 larval lobsters, hence the necessity for a greater or more perfect, 

 defensive transparency. Such, obviously, can be better attained in 

 a thin flattened body, than in a thick muscular one. 



Surely this study of individual development is without superior 

 in fascinating interest among Zoological problems — its interest, too, 

 enhanced by the great light it sheds upon the past development of 

 the race. But while its importance in this sense is so great, let us 

 beware of blind acceptance of that present day biological shibboleth 

 " Ontogeny recapitulates Phylogeny," meaning that the history of 

 the development of the individual sums up and points out the 

 various stages passed through by the particular race in the course 

 of its evolution. Such a theory I doubt not is useful to work by, 

 but it must have intelligent and reasoning and ultra-careful hand- 

 ling, or further false pages will be added to the already too many 

 that have of late years been inserted in our scientific journals by 

 hasty and theory-ridden writers. The harm done in this way is 

 incalculable and unfortunately difficult to cope with or to stem. 

 Every such wildly reasoned generalization or inference is a false 

 finger post upon the scientific highway. Therefore let us beware of 

 setting up even one more. 



Explanation of Figs. 1 and 2, Plate VI. 



The Phyllosoma larva of Scyllarus. 



Fig. 1. Early Phyllosome larva seen from the dorsal surface ; actual 

 length (tip of rostrum to end of abdomen) 1'5 mm. ; 

 e. paired compound eyes ; e\ unpaired simple eye ; c. head ; 

 th. thorax ; ah. abdomen ; I. anterior antennae ; II. pos- 

 terior antennas ; III. mandibles ; IV & V. 1st and 2nd 

 maxillae ; VII & VIII. 2nd and 3rd maxillipeds ; IX, X 

 & XI. 1st, 2nd, and 3rd ambulatory limbs ; XIII. 4th 

 ambulatory limb beginning to sprout ; exp. exopodite ; 

 g. rudiment of green gland ; I. largely lobed liver. 



