193 



The observation mentioned in the preUminary notice may be recalled 

 here, that this species is very often infested with a parasitic organism 

 (Cirripedian?), which castrates its host, the parasite occupying the place 

 of the genital organs of the starfish. 



Pisaster ochraceus (Brandt). 



Among the numerous Asteroids occurring near the Biological Station at 

 Nanaimo, Vancouver Isl., this species is especially conspicuous on account 

 of its remarkable gregarious habits, generally assembling in shoals on rocks, 

 where it may be above the water for several hours during ebb tide; 

 the specimens are very closely aggregated, with interwoven arms. It was 

 found to have ripe sexual products by the end of May, and fertilization 

 was undertaken on May 24th. It was unusual in the spermatozoa being 

 very active in natural sea-water, without addition of NaOH. The eggs are 

 small, not very transparent. The blastula-stage was reached after about 

 24 hours (the ectoderm is not folded) and the gastrula-stage in the course 

 of the second day; at the age of four days the embryos were beginning 

 to assume the Bipinnaria-shape, and at the age of six days they were 

 beautiful small Bipinnariae of typical shape. Although the culture was kept 

 alive and apparently in good health for about four weeks the larvae did 

 not develop beyond this stage; in some of the specimens of this age the 

 enterocoel pouches had begun to grow forwards into the anterior end of 

 the body, but they had not yet fused. 



The shape of the larva is shown in Fig. 100, B (the specimen figured is 

 30 days old); it does not offer any marked special features. The fact that 

 the cihated band of the ventral median process is rather weak indicates 

 that the larva is going to develop into a Brachiolaria. It is pigmented all 

 over with fine, yellow spots. 



Euasterias Troscheli (Stimpson). 

 This species, which is also very common at Nanaimo, although not so 

 much so as the preceding one, (— it may also be found above the water 

 for several hours during ebb tide, but it is not gregarious — ), was likewise 

 found to have ripe sexual products by the end of May. Artificial fertihza- 

 tion was undertaken on May 25th. The eggs are exceedingly numerous, 

 very small, not very transparent; the spermatozoa were very active in 

 natural sea-water, without addition of NaOH. The cleavage stages were very 

 beautiful, perfectly regular. The embryos were not liberated from the egg 

 membrane till after 24 hours, the gastrula stage being reached on the 



25 



