26 



HEMICHORDATA 



system and the anus. Each oviduct (ovd) contains dark pigment, 

 which is seen through the dorsal skin on removing the tentacular 



arms. Eggs, each enelosed in a 

 stalked membrane, occur in num- 

 bers in the cavities of the gelatin- 

 ous house. The early stages of the 

 development are passed through 

 inside the tubes ; but there is at 

 present little other information 

 with regard to the embryonic de- 

 velopment of the Pterobranchia. 

 The specimen obtained by the 

 " Siboga " from Celebes is a male 

 colony with dimorphic individuals, 

 the reproductive organs being con- 

 fined to two-armed zooids with 

 vestigial alimentary canal. 



Rhahdopleura differs from 

 Geplialodiscus in its much smaller 

 size,^ and it is perhaps due to 

 its minuteness that it does not 

 possess certain organs found in 

 the latter. The stalk is repre- 

 sented by a long muscular cord, 

 which is merely a narrow part 

 of the body. Basally the stalk 

 of each individual passes into a 

 common axis, which is for the 

 most part attached to the sub- 

 stance on which the colony is 

 Fig. 12.— Small portion of colony of growing, and is to some extent 



Rhabdopleura normani, Allmaii, hranched The Trrnqpiilnv atnlV 

 Lofoten Islands, v 16. a. Anus; '-'^^^I^Cnea. J.ne muSCUiai Stalk 



j3, proboscis (= buccal disc) ;,-, rod- Can be Contracted into a spiral, 



like axis of the adherent part of the f>,aynlw -^a¥^^^M\^^r, <-!,„ ■ i 



colony, prolonged into s, the stalks thereby retracting the animal 



of the individuals ; st, stomach ; t, intO its tube. The Stalks and 

 the two tentacular arms of the collar, ii, j. r . , 



(After Sars.) the younger parts of the axis 



which connects them are soft, but 

 the older parts secrete a dark brown cuticle, forming a narrow 



' The diameter of a single individual removed from its tube is given by Fowler 

 as '123 mm. 



