No. 10. — On some Points in the Structure of the Erribryonic Zoeci. 



By Walter Faxon. 



The embryonic cuticle which clothes the larvae of the higher Crusta- 

 cea at the time when they leave the egg has been studied with more or 

 less care by Du Cane,* Spence Bate,t Fritz Miiller,J Gerbe,§ A. Dohrn,|| 

 Stuxberg,^ Claus,** and P. Mayer. ft Muller first called attention to 

 the fact that the tail of this embryonic skin in certain genera of Brachy- 

 ura {Achceus^ Maia) resembles that of the larvae of shrimps and prawns, 

 and working upon this hint Mayer has shown the great morphological 

 and phylogenetic value of a careful comparison of the caudal fin of the 

 embryo with that of the following free-swimming stage. 



While in Mr. Agassiz's laboratory at Newport, R. I., in the summer 

 of 1879, I made some observations upon the youngest larval stages of a 

 few Brachyura, especially Carcinus mannas and Panopeus SayL Although 

 the former species is the subject of Spence Bate's elaborate memoir on 

 the development of Decapod Crustacea, I am induced to publish my ob- 

 servations on account of the important discrepancies between them and 

 those of Bate. 



Carcinus m8Bnas.J+ 



The young of this species are peculiarly favorable for a study of the 

 embryonic membrane, since it is often retained for twenty-four hours 

 after emerging from the egg. In most species, on the contrary, the first 

 moult takes place within an hour or so after hatching ; indeed, in the 

 case of Gelasimus pugnax Smith, which I raised from the egg for the ex- 

 press purpose of examining the embryonic cuticle, I have only succeeded 



* Ann. Nat. Hist., Vol. III. p. 438, PI. XI. 1839. 



t Phil. Trans. Roy. Soc. London, Vol. CXLVIII. p. 589, PI. XL. 1859. 



X Fiir Darwin, 1864. Eng. Trans, by W. S. Dallas, p. 53. 1869. 



§ Comptes Rendus, Yol. LIX. p. 1102. 1864. 



li Zeitschr. Wiss. Zool., Vol. XX. p. 621, PL XXX. 1870. 

 1[ Ofvers. Kongl. Vetensk. - Akad. Forhandl., XXX. (1873), No. 9, p. 6. 1874. 



** Untersuchungen zur Erforschung der Genealogischen Grundlage des Crusta- 

 ceen-Systems, p. 62, PI. X. Fig. 9. 1876. 



ft Jenaische Zeitschr., Vol. XL, p. 246, PI. XV. 1877. 



Jt It may not be superfluous to append a list of those who have treated of the de- 

 velopment of this common and widely distributed crab : — 



VOL. VI. — KO. 10. 



