9. Embryo of Astacus fluviatilis just before leaving the egg. The carapace has been cut away from the side 
turned toward the observer, in order to show the gills. The first and last pairs of abdominal appendages 
are undeveloped ; otherwise the embryo has the essential characters of the adult, and undergoes no marked 
metamorphosis after leaving the egg. From Rathke, Untersuchungen tiber die Bildung und Entwickelung 
des Flusskrebses, Taf. I. fig. 16, Leipzig, 1829. 
10. Astacus fluviatilis, two lately hatched young attached by their chelipeds to one of the abdominal appendages 
of the mother. Four times natural size. 6, protopodite ; «, endopodite ; § exopodite of the abdominal 
appendage of the mother. 7, ruptured egg-cases. From Huxley, op. cit., p. 41. 
11. Spermatozoén of Homarus Americanus. From a drawing by Faxon. 
12. Embryo of Homarus Americanus. VIII, third maxilliped. The dotted line rests on the exopod. The longer 
endopod extends beyond the tip of the exopod. The endopods of the succeeding pairs of appendages are 
concealed by the exopods. 4, heart. From a drawing by Stimpson, June 6, 1852. 
13-16. From drawings by Faxon, Newport, R. L., July 18, 1881. 
13. First antenna of embryo of Homarus Americanus just before hatching. The shaded part indicates the 
antenna of the larva seen through the cuticle of the embryo. 
14. Second antenna of the same. 
15. Tail of the same. , median spine of the tail of the first larval stage. «¢, lateral spine of tail of first larval 
stage. All the spines of the enclosed larval tail are shortened by invagination. 
16. Tail of first larval stage of the same. The larva is about to moult, and the tail of the following larval stage is 
seen through the cuticle. 
17. First larval stage of Homarus Americanus. Leaves the egg inthe Mysis condition. Natural size, about 8mm. 
long. From a drawing by A. Agassiz, Nahant, Mass., July 1, 1866. 
18-30. Development of Paguride. 
18. Section of egg of Eupagurus Prideauxii before cleavage. The nucleus has divided into eight, four of which 
are seen in the section. Each nucleus is surrounded by a thin layer of protoplasm which sends out thread- 
like processes into the surrounding yolk. The segmentation is at first total, but after the fourth phase the 
cleavage spheres fuse in the deutoplasmic centre of the egg, and the subsequent cleavage is superficial. 
From Mayer, Zur Entwicklungsgeschichte der Dekapoden. Jenaische Zeitschr., XI., Taf. XIU fig. 1, 
1877. 
19. The same after the fourth cleavage. mc, nuclei surrounded with a layer of protoplasm. From Mayer, op. 
cit., Taf. XIII. fig. 4. 
20 - 23, 25-30. From drawings by Faxon, Newport, R. I, August, 1881. 
20. First larval stage of Pagurus. Leaves the egg in the zoéa form, the first and second maxillipeds serving as 
locomotive organs, the third maxillipeds (VII) present but rudimentary. No thoracic or abdominal 
appendages. The sixth abdominal segment is fused with the telson. The posterior thoracic segments are 
potential merely. 
21. First antenna of the same. 
22. Second antenna of the same. sp, spine. 77, rudimentary flagellum. re, squamiform appendage. 
23. One half of the hind border of the tail of the same, armed with seven sete, the sixth of which (counting from 
inner side) is reduced to a small curved hair. Within the tail, represented by light shading in the figure, 
are seen the caudal sete of the next larval stage. It appears that the inner seta of the first stage will be 
replaced by two (1’, 1) in the second larval stage. 
24. Tail of embryo of Eupagurus Prideauxii. The seta numbered 6, which becomes a rudiment in the first larval 
stage, is well developed. All the sete are feathered except the outer ones, 7. From Mayer, op. cit., Taf. 
XV. fig. 43. 
25. Tail of second larval stage of Pagurus, from Newport, R. I. Comparison with Fig. 23 shows that a new seta (1’) 
has been developed on the inner side of the seven primary setz of the first larval stage. 
26. Mouth parts of the same. 76, labrum. mé¢, metastoma. II, mandible. IV’, IV”, 1V’”, first maxilla. 
vi, Vv", Vv", V”", second maxilla. 
27. Third larval stage of Pagurus. The exopods of the third maxillipeds have become functional swimming 
organs. Rudiments of the chelipeds (IX) and two or three following pairs of thoracic appendages have 
appeared, and they are simple from the time of their first appearance. There is thus a syncopatiom of 
the Mysis stage in Pagurus and in Anomoura generally. In the suppression of the Mysis stage and in 
the late functional development of the third pair of maxillipeds, the dnomowra resemble the Brachyura 
rather than the typical Macroura like Palamonetes vulgaris (see Pl. XI.). In the structure of the second 
antennw, spatulate form of the terminal segment of the abdomen, and the appearance of the posterior 
abdominal appendages (XIX) in advance of the rest, Pagurus agrees in its development with Palamonetes 
vulgaris. XIX, last pair of abdominal limbs. Their inner branch is commencing to grow as a small lobe 
from the proximal end. The sixth segment of the abdomen is now a free segment. 
28. Tirst antenna of the same. 
29. Second antenna of the same. 
30. Telson and appendage of sixth abdominal somite. xe, rudimentary inner branch of appendage. The Arabic 
numerals indicate the correspondence of the sete of the telson with those in the earlier larval stages. 
