PLATE XIII. 
Development of Drcaropa, continued. Figures from Aupxanper Acassiz and Wautrr Faxon. 
br. Gill. Ub. Labrum. re. External branch of appendages. 
et. Embryonic cuticle. mt. Metastoma rt. Internal G ue 
h. Heart. oc, Eye. st. Stomach. 
i. Intestine. r. Rostrum. 
The Roman numerals denote the xppendages of the body in their consecutive order. 
1-9. Development of Paguride (continued from Pl. XIT.). 
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, R. I., August, 1878. 
2. Larva of Pagurus 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 telson 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 (Pl. XII. fig. 23). 
5-9. From drawings by A. Agassiz. 
5. Older stage of a Pagwrus from Naushon Island, Mass., August 23, 1865. 2mm. long. This is the genus 
Glaucothoé of Milne-Edwards, Prophylax of Latreille. 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 appendages 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 Pagurus 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. L, 
July 24, 1876. 
10. Zoéa stage of Porcellana (Polyonyx) macrocheles. First stage after shedding the embryonic cuticle. VIII, 
rudimentary third maxilliped. From a drawing by A. Agassiz, Newport, R. I., August 31, 1865. 
11. Last zoéa stage of the same. 16 mm. from tip of rostrum to tips of posterior horns of carapace. The first 
antenne are now two-branched. The five posterior thoracic appendages (IX—XIIT) are present in a rudi- 
mentary shape, bent up under the carapace. The telson is not distinet from the sixth abdominal somite. 
The second, third, fourth, and fifth abdominal somites carry simple unsegmented appendages. From 
Faxon, On some Young Stages in the Development of Hippa, Porcellana, and Pinnixa, PI. II. fig. 1. 
Bull. Mus. Comp. Zodl., V., 1879. 
12. Third maxilliped of the same stage, more highly magnified. 77, inner branch. re, outer branch. From 
axon, op. cit., Pl. II. fig. 12. 
13. Five posterior pairs of thoracic appendages (chelipeds and ambulatory limbs) of the same stage, removed from 
the body. 07, gills. 
14. Young Polyonyx following at a single moult the zoéa represented in fig. 11. Dorsal view. Length of cara- 
pace, 2mm. _ It has now all the essential characters of the adult. The sixth abdominal 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 natural 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., Pl. 111. 
fig. 11. 
16-18. Carcinus menas. From Faxon, On some Points in the Structure of the Embryonic Zoéa, Pl. I. Bull. 
Mus. Comp. Zool., VI., 1880. 
16. Young just after it leaves the egg (protozoéa stage). 4mm. long. Within the transparent embryonic cuticle 
may be seen the zoéa as it will appear at the next moult. The cuticle of the abdomen is unsegmented, has 
no rostral or dorsal spines, nor appendages back of the second maxillipeds. The two pairs of antenne are 
enormously developed as in nauplii or the protozoéa of Penews, &c. VIII, 1X, 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 the fourteen-spined caudal fork of the lary 
of the lower Decapoda, e. g. Peneus. (See Pl. IX. figs. 14, 18.) The shaded portion represents the tail of 
the following stage, seen through the transparent cuticle. 1/- 5’, spines on the tail of the next (zoéa) stage, 
much shortened by invagination. 4’ becomes the great lateral prong of the tail of the zoéa. (See Pl. XIV. 
fig. 2.) 
18. The same in the process of moulting the protozoéa cuticle. ¢#, 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 zoéa are used 
to tear the embryonic membrane from the anterior parts of the body. The great dorsal spine of the zoéa 
which has been bent down forwards upon the back is now unfolding and lifting the cuticle as it rises. 
