520 PYCNOGONIDA PCHAR: 
in most genera on the last two; in Pycnogonum and Rhynchothorax 
on the last only. 
Very commonly the female individuals are somewhat larger 
than the males, and in some species (Ammothea, Trygaeus) the 
latter are distinguished by a greater development of spines or 
tubercles on the body and basal joints of the legs (Dohrn), 
The act of fecundation has been observed by Cole’ in 
Anoplodactylus. The animal reproduces towards the end of 
August. Consorting on their Hudendriwm (Hydroid) colony, 
the male climbs upon the female and crawls over her head to 
lie beneath her, head to tail; and then, fertilisation taking 
place the while, the hooked ovigerous legs of the male fasten 
into the extruding egg-masses and tear them away. The whole 
process is over in five minutes. The fresh egg-masses are more 
or less irregular in shape, and white in colour like little tufts 
of cotton. 
Each ball of eggs that the male carries represents the entire 
brood of one female, and in Phowxichilidium Loman has seen a 
male carrying aS many as fourteen balls. Fertilisation is 
external, taking place while the eggs are being laid. The 
spermatozoa have small rounded heads and long tails, and are 
thus unlike the spermatozoa of most Crustacea. 
Development.— Until the hatching of the embryo, the eggs 
of the Pycnogons are carried about, agglutinated by cement- 
substance into coherent packets, on the ovigerous legs of the 
males. They are larger or smaller according to the amount of 
yolk - substance present, very small in Phowxichilidium and 
Tanystylum (Morgan), where they measure only ‘05 mm. in 
diameter ; larger in Pallene (25 mm.); larger still (5-"7 mm.) in 
Nymphon. In Pallene each egg-mass commonly contains only 
two eggs; in the other genera they are much more numerous, 
rising to a hundred or more in Ammothea (Dohrn). The egg- 
masses may be one or more on each ovigerous leg, sometimes 
(Phoxichilidium angulatum, Dohrn) a single egg-mass is held 
by both legs; they are extremely numerous in Phowichilus, and 
in Pycnogonum they coalesce to form a broad pad beneath the 
body. The fact that it is the male and not the female that 
carries the eggs was only announced in 1877 by Cavanna ;” 
1 Biol. Bulletin Woods Holl, vol. ii., Feb. 1901, p. 196. 
2 Studi e ricerche sui Picnogonidi, Firenze, 1876. 
