530 THE ANATOMY OF INVERTEBRATED ANIMALS. 



is a long tube (Fig. 151, p,p), which lies on one side of the 

 haemal face of the body and opens on a papilla in the atrium. 

 The ovary, small, rounded, and situated close to the hinder 

 end of the testis, contains many ova. According to Kefer- 

 stein and Ehlers, the ova and spermatozoa appear often to 

 become ripe at the same time. 



The first sexless zooid (B) resembles A in general form, 

 but has nine muscle-rings. The long stolon, which trails in 

 the water, is attached in the seventh intermuscular space to 

 the middle of the neural face of the body. The stigmata are 

 arranged as in the form A, of Doliolum Mulleri, and one of 

 the anterolateral nerves terminates in an otolithic sac. It is 

 spherical, and contains a single otolith. 



The zooids produced by the lateral buds of the stolon (C V) 

 have wide oral apertures, and the body is shaped somewhat 

 like the bowl of a spoon. They possess neither auditory or- 

 gans nor genital organs, nor have they been observed to de- 

 velop buds. The median zooids (C m) closely resemble the 

 sexual zooids. The stalk by which each is attached, and the 

 insertion of which is in the middle line of the haemal face in 

 the sixth intermuscular space, remains as a prominence after 

 the animal is set free ; and, from the base of this prominence, 

 buds are developed which take on a sexual form (A). 



In the Salpoe, the divergence from the ordinary Tunicata 

 reaches its maximum. The oral and atrial openings are situ- 

 ated at opposite extremities of the body, as in Pyrosoma and 

 Doliolum ; and the branchial stigmata are represented by 

 wide vacuities at the sides of the branchial sac, the walls of 

 which are thus represented only by the epipharyngeal folds 

 on the one side, and a narrow trabecula, which occupies the 

 region of the hypopharyngeal band, on the other side. The 

 relatively small alimentary and reproductive viscera are some- 

 times aggregated into a mass — the so-called nucleus — at the 

 posterior end of the haemal side of the body. The chief mus- 

 cular bands, by the contraction of which the water is driven 

 out of the branchial and atrial apertures, and the propulsion 

 of the animal is effected, are transverse, but do not form com- 

 plete hoops, as in Doliolum. 



In all the Salpoe, each species is represented bv two sets 

 of zooids, the one sexual and the other sexless. The sexual 

 zooids are produced by budding from a stolon, which is given 

 oil from the body of the sexless form in the immediate neigh- 

 borhood of the heart. When the sexual zooids thus formed 

 are detached, they are at first connected into chains of vari- 



