PLATE IV. 



a en. Anterior hypoblast cell. 



a n. Anus. 



c e ». Central hypoblast cell. 



c r. Cirrhi. 



e c. Epiblast. 



gen. Beginning of the genital sy.stem. 



i. Intestine. 



to. Labrum. 



/ e n. Lateral cells, containing hypoblastic elements. 



m .«. Cells containing the elements of the mesoblast. 



m t. Metastoma or paragnathite. 



n. Ner\"ous system. 



n'. Secondary supra-ccsophageal nerve-ganglion. 



n c. Nucleus. 



c. Eye. 



ocl. Simple eye. 



oes. Oesophagus. 



ovd. Oviduct. 



p c. Pobir cell. 



p ms. Primitive mesoblast cell. 

 The Roman numerals denote the appendages in their consecutive 



order. See explanation of Fig. 28, infra. 



1 - 5. Development of Cirripedia, continued. Fifjures from Alexander Agassiz and Carii 



Clads. 



1-4. Stages in the development of a Balanus from Kewport, R. I., reared in confinement directly from the larvae 

 represented on PI. IIL figs. 2.3, 24, and sho^ving the metamorphosis of the free-swimming larva into the 

 sessile adult. From drawings by A. Agassiz, Angust 29, 1872. 



1. The bivalve shell of the Cypris stage is becoming split up through calcification into the compartments and 



opercular valves of the adult, c )•, cirrhi, representing the swimming-feet of the Cypris stage. 



2. Later stage, seen from above. The cirrhi are reti-acted within the shell. 



3. Still older stage, side view, h^, tergum. A-, scutum. 



4. Seen from above, cirrhi retracted within the operculum. \^ tergum. \-, scutuin. Surrounding these 



opercular valves are seen the marginal compartmeuts. X', c.irina. A.*, carino-lateral compartment. A', 

 lateral compartment, a", rostrum. 



5. Pupa stage of Lcpas fasciculata. ocl, median eye. o c, paired eye. f, abdomen. I, prehensile antennne. 



From Clans, Die Cyjiris-ahnliclie Larve (Puppe) der Cin-ipedien. Schriften Gesellsch. Beford. gosamrat. 

 Katurwissensch. Marburg, IX., Suppl. 5, Taf I. fig. 2, 1869. 



6 - 28. Development of Copepoda. 



Figures from Carl Glaus, Alexander v. Nordmann, and 

 Carl Grobben. 



• 13. AMhcres percarum. 6-11, l.j, from Claus, ITeber den Bau und die Entwicklung von Achtktrcs perca- 

 rum. Zeitschr. wissensch. Zool., XL, Taf XXIII., XXIV., 1861. 



. Larva at the time it leaves the egg. Only the two anterior pairs of appendages of the typical nauplius are 

 present (I, II), and both of them are simple and unsegmented. Beneath the cuticle may be seen the six 

 following pairs of appendages : mandibles (III), maxilla; (IV), maxillipeds (V, VI), and two jiairs of swim- 

 ming-feet (VII, VIII), which become functional after the next moult, a, frontal papilla, in which is the 

 opening of the coiled canal, 0. This is filled -with a viscid secretion probably brought into play when the 

 larva attaches itself to its host. 



. Mouth-p.irts under the cuticle of the s,ame stage, seen from the side. The lettei-s lb are in the place of the 

 labrum. Directly lielow is seen one of the pair of protuberances which lie on each side of the labrum, fol- 

 lowed by the mandibles (IIIl, maxillje (IV), and two ]iairs of maxillipeds (V, VI). 



. Hinder part of the body of same stage, the cuticle having been removed so as to expose the swimming-feet 

 and the caudal fork. 



