520 PYCNOGONIDA 



in most genera on the last two ; in Pycnogonum and Rhynchotliorax 

 on the last only. 



Very commonly the female individuals are somewhat larger 

 than the males, and in some species {Ammothca, 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 

 Aiioplodactylus. The animal reproduces towards the end of 

 August. Consorting on their Eudeiidrium (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 Phoxichilidium 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 Phoxichilidium and 

 Tanystylum (Morgan), where they measure only '05 mm. in 

 diameter; larger in Pft//e7ig ('25 mm.); larger still ("S-"? 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 angidatum, Dohrn) a single egg-mass is held 

 by both legs ; they are extremely numerous in Phoxichilus, 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 Cavamia;^ 



^ Biol. Bulletin Woods Holl, vol. ii., Feb. 1901, \). 196. 

 ^ Studi e ricerche sui Picnogonidi, Firenze, 1876. 



