52 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DoC. 20, 



2nd stage. — " In more advanced eggs three pairs of rudimentary- 

 limbs were observed, the most anterior pair* being much smaller 

 than the rest. The mouth-opening is situated just behind them." 



3rd stage. — " In a succeding stage [of which Dr. Packard gives a 

 figure] the embryo forms an oval area surrounded by a paler-co- 

 loiTred areola, which is raised into a slight ridge. This areola is 

 destined to be the edge of the body or line between the ventral and 

 dorsal sides of the animal. There ai-e six pairs of appendages, 

 forming elongated tubercles, increasing in size from the head 

 backwards ; the mouth is situated between the anterior pair." (See 

 p. 50, fig. 17.) _ _ . 



4th stage. — At this stage we have figures and descriptions both 

 from Drs. Dohrn and Packard, the former of whom has prepared 

 most excellent plates, the paper of the latter being illustrated by 

 clear, sharp, woodcut outlines only. 



" The oval body of the embryo has increased in size ; the se- 

 paration into cephalothorax and abdomen has taken place ; the 

 mouth-opening is seen, and the rudimentary six pairs of appen- 

 dages are readily made out. The first pair are well marked by their 

 position in front of the mouth and their minute size ; in like man- 

 ner, the sixth pair are distinguished by their greater development 

 and modified form." Dr. Dohrn also detects in this stage the under 

 lipt ; but his drawing does not show it very clearly. This is fol- 

 lowed by the rudiments of the first thoracic plate bearing in the 

 adult the ovaries and marked in the embryo by two pores (x). Behind 

 these come the rudiments of the first two pairs of branchiferous 

 plates, not yet outspread. The abdomen (a) is then, as afterwards, 

 destitute of appendages, (See page 50, figs. 18 & 19.) 



5fh stage. — Dr. Dohrn alone seems to have observed the next suc- 

 ceeding stage. 



He represents the ventral aspect ; in the background we see two 

 bodies only — one being the head-shield, the other the thorax and 

 abdomen (?), or at least their rudiments ; no segmentation, however, 

 is shown in these divisions. (See page 50, fig. 20.) 



The limbs are as well developed as those of an Acarus, which this 

 form somewhat resembles. The antennules are exceedingly small, 

 and have no chelse ; the other limbs appear to be six -jointed and to 

 possess small chelee at their extremities {enclosed in a sheath). The 

 rudimentary bilobed metastoma (under lip) is also to be discerned 

 at the base of the sixth pair of appendages. 



The thoracic plate is now of some size, and, although strongly bi- 

 lobed, is of sufficient extent to conceal the ovarian openings. Two (?) 

 branchiferous plates follow. 



[This was probably the stage observed by Dr. Milne-Edwards in 

 1838, and referred to in my paper. Quart. Journ. Geol. Soc. 1867, 

 vol. xxiii. pi. ii. figs. 3 and 4, p. 34. Dr. Milne-Edwards's descrip- 

 tion seems to ha fully borne out by Dohrn and Packard.] 



P)th stage. — We are rather at a loss whether to consider this a 

 distinct stage. Dr. Packard having seen the dorsal aspect of the em- 

 * The antennules.— H. W. t Metastoma.— H. W. 



