9-17. Devdopment of Nebalia Geoffroti. Figures from Eli as Metschnikoff, IICTOPM 

 PALiBUTM yEBALlA. aAnUCOKl) IIMH. AKA;i,Einil HAXK'b. XIII., CAmiTHTEPByiT'b, 

 1868 [Developuieut of Sebalia. Mem. liiiper. Acad. Sci., XIII., St. Petersburg, 1808]. 



9. Early stage showing partial segmentation (telolecithal). \^. 



10. Later stage. The blastoderm cells now form a cap over one pole of the egg. ^. 



11. So-called naupUus stage of the embryo. The rudiments of the two pairs of antennai and mandibles are present 



(I, II, III), a b, abdomen. 



12. Later stage in the development of the embryo. The seven anterior pairs of appendages are now present. 



lb, labrum. a, anus. 



13. Still older ]ihase. The dotted line from VIII passes a little forward of its proper place in the figure. 



14. Embryo at the time of leaving the egg. Most of the appendages are present. The body is still enveloped in 



a larval skin, cl, and the abdomen is bent upwards. V. 



15. Older larva after the larval skiu has been cast oil". IV', external branch of first maxilla, oc, eye. cp, cara- 



pace. '^. 



16. Later stage, r, rostrum. IV', appendage of the first maxilla extending backwards over the branchial feet. 



Vl-XllI, branchial feet. Behind these are four paii's of abdominal swimming-feet, a h^, eighth somite of 

 abdomen bearing the two terminal styliform appendages ({). ^j^. 



17. One of the phyllopod appendages. 1, inner branch. 2, middle branch. 3, outer branch. ^-^. 



18 - 22. Development of Schizopoda. Figures from Elias Metschnikofp and Carl Claus. 



18. Nauplius of Eiiphatisia, just hatched. A mouth opening is seen between the bases of the third pair of ap- 



pendages, but there is no anal orifice. From Jletschnikofi", L^eber den Naupliuszustand von Euphausia. 

 Zeitschr. wissensch. Zool., XXL, Taf. XXXIV., 1871. 



19. Later stage of the .same, ocl, ocellus, lb, labrum. vit, metastoma or lower lip. IV, rudiment of first 



maxillae. V, second maxilla;. VI, first maxilliped. The carapace is now present. The specimen figured 

 was about to moult, and within the third pair of nauplius appendages are seen the mandibles of the next 

 stage, when the function of these appendages becomes masticatory. From Metschnikoff, op. cit. 



20. Later stage (protozoea) of a Euphausia larva from the Atlantic Ocean, seen from the ventral side. 1^ mm. 



long. The hind body (thorax and abdomen) has now acquired great length. The segmentation of the body 

 is beginning in the region back of the first maxilUpeds, i. e. in the thoracic region, the hinder or abdominal 

 portion being yet uninvaded by segmentation. /, frontal sense-organ, similar to that shown on previous 

 plates in larvie of Cirripcdia, Apus, &c. Grobben (Arbeiten Zoolog. Inst. Wien., II. p. 262, Taf. XVII. 

 figs. 71-76, 1879) has shown that the larva of Eupliausia also lias a "dorsal organ " equivalent to that 

 which we have seen in the embryos of many of the lower Crustacea, i, intestine, a, anus. (, longitudinal 

 muscles of the abdomen. From Claus, Untersuchungeu zur Erforschung der Genealogischen Grundlage des 

 Crustaceen-Systems, Taf. I., 1876. 



21. Still later .stage (zoea) of the same, lateral view. 2J mm. long. The thoracic region behind the first maxil- 



liped (VI) is divided into its full number of seven somites, although they are extremely short. The abdo- 

 men is also divided into six somites. The telson is not yet separated by a suture from the sixth segment. 

 Underneath the cuticle of the anterior portion of the terminal segment are the rudiments of the posterior pair 

 of abdominal appendages (not seen in the lateral view). The larva, unlike the typical zoea, lacks the second 

 pair of maxillipeds, and the antennie are still large swimming-organs. As the development proceeds, the tho- 

 racic and abdominal appendages develop as two independent series from before backwards, the abdominal 

 series being completed before the thoracic series, o c, eye. From Claus, loc. cit. 



22. Second and third maxillipeds (VII, VIII) and the first and second ambulatory appendages (IX, X) of a £■«- 



y/iaima ■li-o mm. long. VII', etc., outer branches of appendages. 6 r, gills. From Claus, ioc. ci<. 



