A STUDY IN MORPHOLOGY. Ill 



at successive moults do not admit of exact comparison with each other ; the outcome, 

 after a few moults, is almost exactly the same, as will be seen by a comparison of 

 fig, GO with fig. 90. 



The number and character of the somites and appendages is now the same, and 

 while the two forms differ greatly in outline and proportion, the young Acetcs is 

 essentially like the young Lucifer, except in the length of the flagellurn of the second 

 antenna, the presence of chelre on the thoracic limbs, the presence of gills, and the 

 absence of a "neck." The outcome of the process of development is alike, but the 

 paths followed diverge from each other to converge again at this stage. 



Comparison of Lucifer and Sergestes. 



The metamorphosis of Sergestes is more like that of Lucifer than is the case with any 

 other known Crustacean except Acetes, but our knowledge of the development of 

 Sergestes is incomplete, and we have no assurance that the various stages which have 

 been described belong to the same species. 



In 1870, DOHRN described a remarkable larva (" Untersuchungen liber Ban und 

 Entwickelung der Decapoden, No. 10, Beitrage zur Kenntniss der Malacostraken und 

 ilirer Larven, Part 4, Beschreibung einer neuen Decapoden-Larve," Zeit. f. Wiss. 

 Zool., xx., p. 607) which he collected at the surface at Messina, and which he was 

 unable to refer to any adult form. He proposed for this larva the provisional name 

 Elaplwcans. Elapliocaris is a Zoea which so far as its appendages are concerned 

 does not differ much from the last Zoca of Lucifer, but its abdomen is very spiny, 

 and the spines on the carapace are drawn out so that each one of them is nearly half 

 as long as the body, and they are fringed with rows of long secondary spines which 

 are hooked at their tips, and so arranged as to give to the body a very grotesque 

 appearance, a.nd the larva does not, at first sight, show any similarity to the simple 

 Erichtliina larva of Lucifer. 



GLAUS had several years before described (" Ueber einige Schizopoden und niedere 

 Malacostraken Messinas," Zeit. f. Wiss. Zool., xiii., 1863) a larval Crustacean with 

 swimrnerets, biramous thoracic limbs, and a very spiny body, which he calls an 

 Acanthosoma. This same larva, or a very closely related form, had been figured and 

 described nearly twenty-five years before by DANA (' Crustacea/ p. 664, plate 44, 

 fig. 5) as Sceletina armata. 



In the same paper GLAUS gives a figure of a young Crustacean, which had previously 

 been described by LEUCKART under the name of Mastiyopus, and shows that it is in 

 all probability a young Sergestes. 



In his ' Untersuchungen zur Erforschung,' &c., he describes an Elapliocaris at a 

 much younger stage than DOHRN'S figure, and shows that this larva, DOHRN'S 

 Elapliocaris, his own Acanthosoma, and LEUCKART'S Mastigopus are successive stages 

 in the development of Sergestes. 



