LIFE-HISTORY OF THE ROCK BARNACLE. 85 



on the dorsal side in front and behind. It measures on the average 

 about 0'7 mm. in length.. 



After swimming about for a certain length of time the larva 

 becomes attached to the rock between tide-marks, and undergoes a 

 very remarkable series of changes which result in the production of 

 a form totally different in appearance from the Pupa. The appear- 

 ance of the young Barnacle when some time after fixation is shown 

 in Fig. 29 ; the shape and colour of the carapace has altered consi- 

 derably ; the changes during this transformation are very considerable, 

 and when the moult has taken place, and the cuticle been finally 

 thrown off, give the young Barnacle almost the form of the adult 

 (Fig. 20). The shell is marked by the same punctures (Fig. 21) as 

 were seen in the Cypris-stage. Further growth in size and some 

 change in the proportion of the parts gradually lead the young form 

 up to the adult. 



(To be continued). 



Note. — The Plate illustrative of Part II of this paper will comprise Figs. 21 to 

 29, references to some of which are made in the text. 



Explanation of Plate VIII. 

 Nauplius-stage of Barnacle. 



Fig. 1. Side view of Nauplius of Stage II of Balanus perforatus. 

 Behind the brain (br.) are seen the circum-cesoph. con- 

 nectives and the sub-cesoph. ganglion. 



Fig. 2. Antennule of same. 



Fig. 3. Antenna of same, with (gn.) gnathobase moved by a 

 powerful muscle (gn. m.) 



Fig. 4. Mandible of same. 



Fig. 5. Distal lobe of labrum showing the four unicellular glands 

 (ax. gl.) 



Fig. 6. Fronto-lateral glands of one side of same. 



Fig. 7. Striated muscular fibres of appendages, showing the muscle 

 corpuscle. 



Fig. 8. Dorsal view of brain of same. 



br. brain ; br. a. I. accessory lobes of brain ; br. c. I. central 

 lobe of brain ; c. o. c. circum-cesophageal connectives ; 

 /. /. frontal filaments arising from spherical bases within 

 the brain ; JVp. e. Nauplius-eye imbedded between two 

 cushions of special sensory cells. 



Fig. 9. Diagrammatic sagittal (median longitudinal vertical) section 

 through Nauplius belonging to Stage II ; int. intestine 

 suspended by contractile fibres ; gt. I. m. longitudinal 



