

ON OUR PRESENT KNOWLEDGE OF THE CRUSTACEA. 197 



insects, and as a further consequence to considerable inquiries about the 

 origin of Crustacea. 



The importance of obtaining accurate knowledge of the relationship of 

 the young and immature forms with those of the adult animals, is exem- 

 plified by the numerous speculative theories which have arisen and depend 

 upon the correctness of Fritz- Miiller's discovery. 



Claus, in his ' Crustaceen Systems,' says that Fritz-Muller even 

 believed that he found in the Zoaea of Crustacea the origin of the insects, 

 and very soon this view was made use of by others for the Arachnoidea. 



"Anton Dorhn," says Claus, " has endeavoured by peculiar reasoning ' 

 to prove the Zoaea form to be a stage in the development of the Ento- 

 mostraca, and sought to show that the Phyllopodes, Ostracodes, and Co- 

 pepoda have once passed through a free Zoaea stage during the phylogmatic 

 development." 



Claus distinguishes two more typical stages in the metamorphosis of 

 Crustacea between Nuuplius and Zoaa, which he distinguishes by the 

 names of Metanauplius and Protozoeil ; but as these are given to stages in 

 the progress of development rather than to forms that represent the stages 

 as they leave the egg and become free creatures, I doubt if this addition 

 to the nomenclature will ultimately be found to prove convenient. He 

 moreover contends that of all Crustacea now existing that of the Phyllopoda 

 is most probably that which bears the nearest resemblance to the primordial 

 type, and that Nebalia and Bmnchipus most nearly approximate the earliest 

 representations. 



In the Schizopoda and Peneidce the larva he asserts is hatched as a 

 NaupUus, and undergoes its further development in free life ; the rest of 

 the Caridea go through the Nauplius and Protozoaea stages within the 

 ovum, and that the first stage of free life is that of the Zoaea, mingled with 

 features of the Mysis-like stage. The Thalassinidae and Paguridae are 

 hatched in the Zoaea stage. 



In the course of his researches Dr. C. Claus has determined the early 

 forms of Leucifer and Sergestis, neither of which, although Schizopods, 

 pass through the Nauplius condition, and Professor Sars says that Lophi- 

 gaster, one of the Euphausidce., develops its young as Mysis. And we 

 know from actual observation that the young of the Anomura leave the 

 ovum in a form little distinguishable from the Zoaea of the Brachyura, and 

 in a more advanced condition. 



It is desirable in a Report which is intended to record the present state 

 of our knowledge of the subject, to define clearly what is understood by 

 the several names applied to the larvae of Crustacea according to the form 

 in which they quit the ovum. 



Here I feel it a duty to protest strongly against the terms larva and 

 pupa which have of late been much introduced into the study of carcino- 

 logy. They are the more objectionable at this present time when there 

 is a desire to trace the connection of one class of animals with another, 

 inasmuch as the terms are likely to convey the idea of a closer approxi- 

 mation by the resemblance of the nomenclature than may exist in natural 

 phenomena. The term larva is suggestive of the grub or caterpillar con- 

 dition in which insects leave their ovum, but as the condition in which the 

 young of the Crustacea varies in form and degree, is not only different in 

 families but in animals that might be classified as belonging to the same 

 genus, as is the case in Crangon vulgaris and Crangon horeas, but for the 

 different stages in which the young are hatched. 



