PLATE XIII. 

 Beoelopmeni of DECAPonA, continued. Figures from Alexander Agassiz <in(l Walter Faxon. 



i i: Gill. I b. Lalirum. r e. External branch of appendages. 



cl. Embryonic cuticle. mt. Metastonia ft- Internal " " 



A. Heart. uc. Eve. St. Stomach. 



i. Intestine. '•. Kostrum. 



The Knnian numerals denote the appendages of the body iu their consecutive order. 



1-9. Development of Paguridce (continued from PI. XII. ). 



1. Larva of Pagurus, from Newport, R. I. Later stage than the one represented by fig. 27 on the previous plate. 



Viewed from the dorsal side. The abdomen now carries five pairs of appendages, on the second to the sixth 

 somites. From a drawing by A. Agassiz, Newport, R. I., August 4, 1875. 

 2-4. From drawings by Faxon, Newport, E. 1., August, 1878. 



2. Larva of Paijurus of about the same age as the one represented by fig. 1. Lateral view. 



3. The same, ventral view. 



4. One half of the hind border of the tclson of the same. Seta 4 has become very short, so that the armature of 



the telson at first sight appears to be the same as in the first larval stage (PI. XII. fig. 2.3). 

 5-9. From drawings by A. Agassiz. 



5. Older stage of a Pagurus from Naushon Island, Mass., August 2.3, 1865. 2| mm. long. This is the genus 



Glaucothoe of Milne-Edwards, Prophylax of LatreiUe. The two sides of the body and the appendages are 

 still symmetrical, except in the greater development of the chela of the right side. The two posterior pairs 

 of thoracic appenilages are much shorter than the anterior pairs. All the abdominal somites bear append- 

 ages except the first. 



6. Abdomen of the same, from the ventral side. 



7. One of the abdominal appendages of a little older stage, when the abdomen begins to curl to one side. 



8. Young Piigurus from Newport, R. I., August 23, 1875, at the age when it takes up its abode in a Molluscan 



shell. 



9. Abdomen of a little younger specimen than fig. 8, showing the atrophy of the curled side. Newport, R. I., 



July 24, 1876. 



10. Zoea stage of Porcdlana [Po/yony.v) macrocMhs. First stage after sliedding the embryonic cuticle. VIII, 



rudimentary third maxilliped. From a drawing by A. Agassiz, Newport, R. I., August 31, 1865. 



11. Last zoea stage of the same. 16 mm. from tip of rostrum to tips of posterior horns of carapace. The first 



antenna are now two-branched. The five posterior thoracic appendages (IX-XIII) are present in a rudi- 

 mentary shape, bent up under the carapace. Tlie telson is not distinct from the sixtli abdominal somite. 

 The second, third, fourth, and fifth abdominal somites carry simple unsegmented appendages. From 

 Faxon, On some Young Stages in the Development of Hijtpa, Poixelkma, and Pinnixa, PI. II. fig. 1. 

 Bull. Mus. Comp. Zool., V., 1879. 



12. Third maxilliped of the same stage, more highly magnified, r i, inner branch, re, outer branch. From 



axon, op. cit., PI. II. fig. 12. 



13. Five posterior pairs of thoracic appendages (chelipeds and ambulator)' limbs) of the same stage, removed from 



the body, b r, gills. 



14. Young Poll/onyx following at a single moult the zoea represented in fig. 11. Dorsal view. Length of cara- 



pace, 2 mm. It has now all the essential characters of the adult. The sixth ajidominal segment is now 

 separated from the telson by a movable joint, and bears a pair of appendages (XIX). From a drawing by 

 A. Agassiz, Newport, R. I., August 30, 1865. 



15. Adult specimen of the same, from South Carolina, twice the natui'al size, viewed from above. Observe the width 



of the carapace compared with that of the young stage represented by fig. 14. From Faxon, op. cit. , PI. 111. 

 fig. 11. 

 16-18. Carciniis mccnas. From Faxon, On some Points in the Structure of the Embryoiuc Zoea, PI. I. Bull. 

 Mus. Comp. Zool., VI., 1880. 



16. Young just after it leaves the egg (protozoea stage). J mm. long. Within the transparent embryonic cuticle 



may be seen the zoea as it will appear at the next moirlt. The cuticle of the abdomen is unsegmented, has 

 no rostral or dorsal spines, nor appendages back of the second maxillipeds. The two pairs of antennae are 

 enormously developed as in nauplii or the protozoea of PcTieiis, &c. VIII, IX, X, third maxilliped and first 

 two ambulatory appendages of the adult, seen through the cuticle. 



17. Caudal fin of the same stage. The tail is forked and bears on each side seven spines (1-7). At this .stage the 



tail of the Brachyuran larva can be compared part for part with tlie fourteen-spined caudal fork of the larvse 

 of the lower Decapoda, e. g. Pcncus. (See PI. IX. figs. 14, 18.) The shaded ]>ortion represents the tail of 

 the following stage, seen through the transparent cuticle. 1'- 5', spines on the tail of the next (zoea) stage, 

 much shortened by invagination. 4' becomes the great lateral prong of the tail of the zoea. (See PI. XIV. 

 fig. 2.) _ 



18. The same in the process of moulting the protozoea cuticle, ct, cuticle peeling off from the abdomen. After 



the cuticle has fallen off from the tail the little hooks which terminate the caudal fork of the zoea are used 

 to tear the embryonic membrane from the anterior parts of the body. The great dorsal spine of the zoea 

 ■which has been bent down forwards upon the back is now unfolding and lifting the cuticle as it rises. 



