CRUSTACEA. 
269 
Third, the mimbcr of appendages found within the ovum ; 
and. suggests the annexed table as a basis of classification. 
Class CRUSTACEA. 
Subclass I. IIOLOSCHISTA.“ 
Complete division of yelk. No primitive stripe. Nauplius group. 
Order I. Ceratometopa. , 
Nauplius with frontal horns. (Cirripedia j Sacculinidae.) 
Order II. Leiometopa. 
Nauplius without frontal horns. (Copepoda, except Achtheres, &c. j 
Phyllopoda, Penaeus.) 
Subclass II. HEmscHiSTA. 
Incomplete division of yelk. 
A. Nototbopa. Embryo rolled outwards. 
Order III. Pbotbusa. Tail formed first. (Mysis.) 
Order IV. Saccomorpha. Worm-like larval skin first formed. (Isopoda.) 
B. Gasteropoda. Embryo rolled inwards. 
Order V. Zoeogona. Appendages not fully developed in the ovum. Zoea 
group. (Most Podophthalma.) 
Order VI. Ametadoda. Appendages perfectly developed in ovum. (Astacus; 
Qecarcinus; Amphipoda, except Ilyperia.) 
That the necessity of the reconsideration of the classification 
of the Crustacea is every day becoming more apparent, we admit ; 
but there are other points in the history of the animals that are 
to be taken into consideration, and require further elucidation, 
besides the embryonic development, which, to say the least, 
would be one of the most inconvenient features to accept, since 
it must necessarily preclude the possibility of fossil Crustacea 
being adopted into the system. 
XI. & XII. are occupied with the discussion of the bearing 
of his own and others^ researches concerning the development of 
Crustacea on the theory of Mr. Darwin ; and he arrives at the 
conclusion that the great variation among the larvae of Crustacea 
in which there is the existence of a continuous similarity in 
parts of minor importance, is presumptive evidence that they all 
descended from one original ancestor, not in a direct line of 
succession, but each under circumstances favourable to itself. 
If the ideas of Dr. Muller be based on truth, it must follow 
as a necessary consequence that the development of the lost 
forms of Crustacea must, the more anciently they existed, have 
departed less from the primitive type than those of a recent 
fauna, and consequently more frequently have quitted the ovum 
in the Nauplius form than in that of the Zoea or perfect form. 
