xviii NOTES ET REVUE 



Tlii' chid' rcsulls of Llicsc stiulies are liciv siiiiiiiiai-ized. 



OôGENESis. Tlie oocylos of l*h. vulgnre and ol' /*//. Gouldii, as is 

 wcll-known, becouie dctachod frum llic ovary or génital cord and 

 fall into tlie cœloni, wliere lliey increase insize from 2."> u. lo 180 \j. 

 in dianieter. The nucleus incanwliile occnpies a central position- 

 Tlie spherules of basichromatin wtiich are scattered tlirougli the 

 nucleus increase in size and abundance ; granules of oxycliro- 

 matin become collected together in transitory nucleoli. A dense, 

 finely granular layer of the cytoplasui iuiinediately surrounding 

 the nucleus extends gradually toward the surface of the egg. 

 Radiating lines of granules pass outward from this layer through 

 the superficial cytoplasm, and are evidently prolonged into the fine 

 protoplasmic processes which surround the egg. The chitinous 

 vitelline membrane becomes secreted around the proximal extrem- 

 ities of thèse processes, thus producing the pore-canals of the 

 zona radiata (vitelline membrane). 



The egg of Ph. elongatum Kef. is ovoid, like a hen's egg, more 

 opa([ue than that of Ph. oulgare and of a greater spécifie gravity. It 

 is surrounded for a considérable lime by follicular cells, which 

 partially cover its perforated vitelline membrane. This egg is 

 unlike that of the Ph. elongatum upon which Selenka's ' observa- 

 tions at Villefranche were made, which is spherical. The develop- 

 ment of the Ph. elongatum of RoscofT, which is evidently the 

 species which Keferstein ^ originally described from spécimens 

 collected at St. Vaast, difTers also in several respects from that 

 of the southern form (e. g. in the absence of latéral bristles in 

 the larva, etc.). 



Breeding Season and Egg-laying uabits. The breeding season of 

 Ph.vulgare at RoscofT extends from the middle of June to the middle 

 of September. Ova that are ready for maturation, having the first 

 polar spindle in the metaphase,are swept from the cœlom into the 

 nephridia by the action of the cilia of the nephrostome. In the 

 mah", mature spermatozoa, which are inactive until extruded into 

 the sea-water, are in like manuer driven into the nephridia. Sper- 

 matozoa are ejected in cloud-like jets through the nephridiopores. 

 Contact of the spermatozoa with the skin stimulâtes the mature 



' Selenka, e. Eifurchung und Larvenbildung von Phascolosoma elongalum Kef. 

 (ZeiLsch. fût-, wiss. Zoologie, x\v Bd., p. 442-450, Taf. xxix-xxx, 1875). 



* Zeilsch. fur wiss. Zoologie, xii Bd., 1863. 



