1868.] 



367 



[Packard. 



32e 



ments, the terminal one being much the hirger, and obscurely divided 

 into two obtuse lobes. 



The abdominal .sterna (urites) are now well marked, and the ner- 

 vous cord is represented by eight or nine large oblong-square (seen 

 sideways) ganglia, which lie contiguous to each other. 



The formation of the eyes, the post-abdomen, the sterna, and me- 

 dian portion of the nervous cord seems nearly synchronous with the 

 closing up of the dorsal Avails of the body over the yolk-mass, though 

 the division of the tei-gum into segments has not apparently taken 

 place. 



4. The succeeding stage (Fig. 2; 

 compare Zaddach's fig. 40) is signal- 

 ized by the appearance of the rudi- 

 ments of the intestine, Avhile the 

 second maxillje are directed more 

 anteriorly. 



In form the body is ovate-cylindri- 

 cal, and there is a deep constriction 

 separating the post-abdomen (as we 



may call the temporary sub-division . , , . , 



„ •^, , , 1.1 11 -^'^ embryo much farther ad- 



ot the abdomen, which would seem to vaneod. c, clyppus, forming a part 



be nerninnentlv retnined in tbf s(>ovni- °^ ^-''^ " procoplialic lobe;" E' 

 oepcimancniiy rciamtu m ine stoipi- g^^. ^^ bi-lobod extremity of the 



ons and some of the higher Crustacea, abdomen; i, the rudiments of the 

 TT i. 1 -r i- J.^ intestines. 



Homarus, etc., where it lornis the ex- 

 pansion at the tip of the abdomen) from the anterior part of the 

 abdomen. 



The terminal (lltli) ring is immensely disproportioned to its size 

 in the embryo just previous to hatching (see Fig. 4 where it forms 

 a triangular piece situated between its appendages, the anal stylets). 

 At a later period of this stage two more abdominal segments have 

 been added, one to the end of the main body of the abdomen, and 

 another to the post- abdomen. They have been apparently interpolated 

 at the junction of the post-abdomen to the abdomen proper. Should 

 this observation be proved to be correct, it may then be considered as 

 a rule that, after reaching a certain number of segments, all additional 

 ones are interpolated between the main body of the abdomen and its 

 terminal segment or segments. This is the law of increase in the 

 number of segments in Worms, and in Myriapods (lulus, according to 

 Newport's observations), in Arachnids (Claparede), and Cinistacea 

 (Rathke). 



5. This stage (Fig. 3), is characterized by the differentiation of the 

 head into the ophthalmic ring, or its rudiments, the eye-bearing piece, 

 and the supra-clypeal piece, and clypeus, together with the approx- 



