THE DOLIOLUM. 



529 



or stolon, from which buds are developed. These buds are 

 arranged in three rows, two lateral and one median, and grow 

 into zooids of two different forms, of which the median may 

 be indicated by C m, the lateral by C I. All these zooids are 

 detached, and swim about as independent organisms. What 

 becomes of the lateral zooids (C /) is unknown. But the 

 median zooids give off a stolon from the haemal side of the 

 body on which buds are developed, which pass into the sex- 

 ual form (A). 



The sexual zooid (A) (Fig. 151) is shaped like a cask with 

 an opening at each end ; these are the oral and cloacal aper- 

 tures. According to Keferstein and Ehlers there is no test, 

 the outer wall of the body being formed, as in most Appen- 

 dicidarioe, by the ectoderm. Eight muscular bands encircle 

 the body, and by their contractions expel the water from 

 either the oral or the cloacal ends. The body is thus pro- 

 pelled either backward or forward. The branchial sac is 

 much simplified. In Doliolum Mulleri, the atrial cavity does 

 not extend further forward than the hinder end of the wide 

 pharynx, and this is perforated only by two rows of stigmata, 

 four or five in each. In Doliolum denticulatum (Fig. 151), 

 on the other hand, the atrial cavity extends forward at the 

 sides of the pharynx, both on the haemal and the neural side, 

 and the stigmata are numerous and vertically elongated. 



An opening in the middle line of the haemal face of the 



Fig. 151.— Doliolum dentin/latum.— a, ganglion: c. endostyle ; tf, oral opening; g, 

 oesophagus; £, stomach; I, intestine; p,2?, testis; r, heart; t,t, muscles. 



pharynx leads, by a short gullet, into a dilated stomach, 

 whence the slender intestine proceeds to terminate in the 

 atrial cavity. The nervous ganglion is situated in the third 

 intermuscular space in D. denticulatum. There is a ciliated 

 sac, but no auditory organ, in the sexual form. The testis 

 23 



