40 THE VOYAGE OF H.M.S. CHALLENGER. 



species, a tliird, ■\vhich, however, he did not name. It has since been described by 

 Grobben ^ as Doliolum rarum. Keferstein and Ehlers added no new species to the 

 list, but erroneously regarded the Doliolum ehrenhergii of the Mediterranean, which 

 they investigated, as being Doliolum denticulatum. 



For a long period subsequent to Keferstein and Ehlers' work no further investi- 

 gations were made upon Doliolum. More recently, Fol, Grobben, Uljanin, and others 

 have by their important observations done much to complete our knowledge of the 

 structure and development of the various species, and to work out the details of the 

 complicated life-history which is now known, thanks mainly to the investigations of 

 Grobben^ and of Uljanin," to be as follows : — 



The embryo becomes a tailed larva which develops into an asexual form known as 

 the " Nurse " (" Amme "), which I propose should be named Blastozooid. This asexual 

 form is characterised by having nine muscle bands round the body, the stigmata 

 few in number and confined to the posterior end of the branchial sac, an auditory organ 

 on the left side of the body, a ventrally-placed gemmiparous stolon close to the heart, 

 and by the possession of a dorsal outgrowth from the body which is directed back- 

 wards (PI. III. fig. 9). The young buds formed on the ventral stolon migrate across 

 the body, and become attached to the dorsal outgrowth in three rows, a median and 

 two lateral, and then proceed to develop into the members of the second generation, 

 the blastozooid which produced them being the first. 



The second or sexual generation is polymorphous, and includes three distinct forms, 

 which are known as nutritive forms, foster forms, and reproductive forms. For these I 

 propose the names Gastrozooid, Phorozooid, and Gonozooid respectively. The nutritive 

 forms (gastrozooids) are produced from the lateral buds. They remain attached to the 

 dorsal outgrowth of the body of the nurse, and serve to supply it with nutriment. 

 They differ consideraljly in appearance from the other forms of Doliolum, and their 

 reproductive organs remain undeveloped. The foster forms (phorozooids) have the 

 ordinary barrel-shaped body, surrounded by eight muscle bands. They are set free from 

 the nurse, but always retain as a ventral outgrowth the remains of the stalk by means 

 of which they were formerly attached. On this ventral outgrowth develop the buds 

 which produce the third form of the same generation, viz. the reproductive animals. 

 These buds of the reproductive form do not originate on the ventral outgrowth of the 

 foster forms, but are derived from the proliferation of the original buds formed on the 

 stolon of the blastozooid, and therefore belong to the same generation as the foster 

 forms on whose bodies they afterwards develop. The reproductive forms (gonozooids) 

 are very like the foster forms in appearance, but have no ventral process. Finally, 



1 Arleit. d. zoolog. Iiixiil. c. Wiai, Bd. iv. lift. '2, 1882. 



- Doliolum und sein GeiioratioDSwecbsel, &c., Arbeit. J. zoclor/. Inst!/. :. Wiei), Bd. iv. Hft. 1. 



^ Fauna u. Flora d. Golfes v. Neapcl, Jlonogr. x., Doliolum. 



