34 



Limulus, afforded by specimens preserved in alcohol, transmitted to him by Dr. Packard. 

 They are confirmatory of the accuracy of the observations of the able American em- 

 bryologist as detailed and illustrated in the work above cited. Dr. Dohrn premises 

 a German translation of Dr. Lockwood's memoir in the ' American Naturalist,' and of 

 the ' Abstract ' (which appeared in the same periodical) of Dr. Packard's Memoir. The 

 chief characteristic of the contribution by the German carcinologist lies in tlie point 

 of view which he has taken of the phenomena. It is a development of that sketched 

 out as follows, in my ' Lectures on Crustacea ' of 1843 and 1868. " To what end, 

 it may be asked, tends all this discussion concerning the affinities of animals that 

 have long ceased to exist ? How are we concerned with it in considerations relative to 

 the generation and development of the actual Crustacea ? To this I have to answer, that 

 it is only by a knowledge of the transitional larval forms of these that we come rightly 

 to comprehend the nature and affinities of the extinct Trilobites, and that our Jcnoioleclge 

 of the most interesting relations of actual larva requires a previous knowledge of the 

 forms of their class that have heretofore existed on this planet " *. This view is developed 

 and illustrated, with large assumptions, as follows, by Dr. Dohrn : — " Fritz Mullcr him- 

 self made the first decided application of this ' law,' viz. that the embryological develop- 

 ment was nothing more or less than a short, though not always exact, recapitulation 

 of the history of all the ancestors of the organism in question — by tracing the different 

 orders of the Crustacea back to their common ancestor, the famous Nauplius, that 

 little crustacean larva that quits the egg and is afterwards gradually developed into the 

 well-known diversified and more highly organized forms " f. 



It may not be out of place here to recall what is understood in plain matter of fact by 

 tlie term Nauplius, as contrasted with its transcendental signification. 



The young of Entomostraca, with ciliate natatory limbs (cuts, figs. 9 & 10) more or less 

 like those of the parent, want, when hatched, the protective bivalve-like cephaletral 

 shield and some other parts of the adult, yet soon show characters which enable the 

 student of the group to refer them to their species, the full diagnosis of which they yield, 

 as in Limulus, after successive ecdyses. 



The first systematic observer of the small representatives of the subclass +, not knowing 

 the genetic relations of his subjects, referred the young of some species to distinct genera 

 — those of Cyclops ( Canthocamptus') minutus e. g. to a genus Amymone, and the hexapod 

 stage of Cyclops quadricornis to a genus Nauplius. Later observations have led to these 

 larvte being relegated to their proper genera and species §. Nauplius saltatorius, 0. P. M. 

 (fig. 10), is the young of Cyclops quadricornis; Nauplius bipes (fig. 9) is the larva otApus 



j)odcn, I. Cumacccn,' 8vo; 'II. P3'cnogonidcn ; ' 'III. Daphnioe,' 8vo, 18G9; 'Die Schalendriise u. embryon. 

 Entwicklg. d. Daphnicn,' 8vo, 1809 ; ' Uebcrrcstc d. Zoeaatadiums in d. ontogciict. Entwickcl. d. verscliied. Crustac- 

 Fam.' Bvo, 1870; ' Untcrs. iib. IJau u. Entwick. d. Artbi'opoden,' I. & II., 8vo, 1870. 



* ' Lectures on Invertebrata,' 8vo, cd. 1855, p. 333. 



t Dr. A. Dobrn, in the ' Academy ' for Nov. 1, 1871, p. 429. 



J ' Entomostraca, sou insccta testacea, quae in aquis Dania; et Norwegia3 rcperit, dcscripsit ct iconibus illustravit, 

 Otho Fred. Muller,' 1785. 



§ See tlie excellent work 'The Natural History of the British Entomostraca,' 8vo, 1850, by W. Baird, 

 M.D., F.L.S. 



