PLATE I. 
1-16. Development of Pycnocontps. Figures from Anton Dourn, P. P. C. Honk, and Grorce 
Hopes. 
ab. Abdomen. r. Proboscis. 
n. Nerve-ganglion. a. Spine on first segment of first pair of appendages. 
oc. Eye. 8. Rectum. 
The Roman numerals indicate the appendages in their consecutive order. 
1, 3-14, from Dohrn, Untersuchungen tiber Bau und Entwicklung der Arthropoden. 2. Ueber Entwicklung 
10. 
De. 
12. 
13. 
14. 
15. 
16. 
und Bau der Pycnogoniden. Jenaische Zeitschr., V., Taf. V., VI., 1870. 
. Egg of Pycnogonwm littorale after cleavage. The nuclei are seen within the cleavage-spheres. Double egg- 
membrane. 
. Section of segmented egg of Nymphon brevicaudatum, hardened in absolute alcohol, and colored with picro- 
carmine. The protoplasm and deutoplasm have not yet separated, and the cleavage is total. Hach 
segment has a nucleus. The faint lines within the segments denote the yolk particles, which appear as if 
vesicular, an appearance perhaps caused by the action of the alcohol. The egg is furnished with a distinct 
but very thin membrane. From Hoek, Report on the Pycnogonida of the Challenger Expedition, Pl. XIX. 
fig. 3, London, Edinburgh, and Dublin, 1881. 
. Egg of Pycnogonum littorale at a later stage than fig. 1. I, I, III, rudiments of anterior three pairs of 
appendages of embryo. 
. Embryo of the same, later stage. 7, proboscis. 
. The same, later stage, profile view. oc, eye. a, spine arising from base of first pair of appendages. 
. Nearly fully developed embryo of the same, from ventral side. 
- Hatched larva of the same, ventral view. The protonymphon stage of Hoek. The anterior pair of append- 
ages is chelate, and the two following pairs are furnished with a sharp terminal claw. The spine on the 
first pair of appendages emits a byssus-like thread secreted by a gland in the proximal segment of the 
appendage. This thread probably serves to fasten the larva to the ovigerous legs of the adult. 
. Eye of larva of Achelia levis. 
. Intermediate stage between larva and adult of Achelia levis, The three pairs of appendages of the larva have 
become much reduced, especially the second and third. The spine (a) on the mandible is disappearing. 
The fourth and fifth pairs of appendages (IV, V) are well developed, and behind them are seen the rudi- 
ments of the two remaining pairs (VI, VII) as lateral outgrowths of the body. The mouth at the end of 
the proboscis leads into an esophagus provided with masticating apparatus (seen at the base of the pro- 
boscis in the figure). The intestine sending diverticula into the appendages is represented by heavy 
shading. £8, rectum. a6, abdomen. 21~—7+4, first to fourth sub-cesophageal nerve-ganglia. 
The same, older. The proboscis has increased in size. The spine on the mandible has disappeared. The 
second pair of appendages has lost its claw. The third pair is reduced to a short stump, which develops 
again in the male into the ovigerous or accessory appendages. The sixth and seventh pairs have attained 
their complete form. 75, fifth sub-cesophageal nerve-ganglion. 
Second appendage (palpus) of adult male Achelia levis. 
Third appendage (ovigerous or accessory) of the same. 
Second appendage of female. 
Third appendage of the same. 
Adult Achelia levis, dorsal view. At the base of the palpi is seen the oculiferous tubercle bearing the eyes. 
From Hodge, List of the British Pycnogonoidea, with Descriptions of several new Species. Ann. Mag. 
Nat. Hist., [3.] XIII., Pl. XIII. fig. 12, 1864. 
Adult Nymphon gracile. The three pairs of larval appendages are now represented by I (antenne, pedipalpi, 
or mandibles, of authors), II (palpi), and III (ovigerous or accessory appendages). The anterior pair are 
innervated from the supra-cesophageal ganglion, and may be homologous with the antenne of Crustacea. 
The second and following pairs receive nerves from the sub-cesophageal ganglia. The third pair of append- 
ages serves, in the male, to carry the eggs. The nervous system is represented by the dotted lines. From 
Hoek, Ueber Pyenogoniden. Niederlindisches Arch. Zool., III., Taf. XVI. fig. 18, 1877. 
