A TAXONOMIC STUDY ON PYROSOMA. — METCALF AND HOPKINS. 235 



Gonads. The production of germ cells commences usually before 

 the zooid has reached its full development, and only after the embryo 

 is set free does the parent zooid complete its growth. Protogyny is 

 the rule for this species, the egg in the majority of zooids maturing 

 before the testis. Neumann (1913, b) in working over this species 

 found that the egg tends to ripen at about the same rate in all the 

 zooids. This is unlike the condition in P. verticillatum, where the 

 egg comes tardily to maturity in the primary ascidiozooids and 

 develops more and more rapidly in each succeeding whorl of zooids, 

 "until a certain stage is reached." In P. aherniosum the primary 

 ascidiozooids ripen their eggs first in almost every case, then the 

 succeeding whorls of zooids ripen theirs, in the order of their prox- 

 imity to the primary zooids; that is, in the order of their age. After 

 the embryo is set free from the ovary it completes its brood develop- 

 ment in the right peribranchial sac. 



Seeliger finds in a large number of his specimens that there are but 

 three primary ascidiozooids at the closed tip of the colony, in place 

 of the usual four, a condition arising through the atrophy of one of 

 these four original buds. He suggests that there may be a tendency 

 here for a distinct variety to establish itself, one characterized by 

 the presence of only three definitive, primary ascidiozooids. Similar 

 freaks have often been noted in other groups of animals, as penta- 

 merous jellyfishes. 



Distribution and occurrence. — This species, although rather 

 recently discovered, has proven to be of rather common occurrence 

 in the Atlantic Ocean, where it was first found. It has been reported 

 since from the Indian Ocean from six stations. Herdman (1888) 

 has described and figured a small Pyrosoma from the western Pacific 

 Ocean which he took to be the "P. elegans" of Lesueur. It seems 

 more probable that he was dealing with specimens of P. aherniosum; 

 this is the opinion expressed by Seeliger and by Neumann, who have 

 worked most on this form. 



PYROSOMA OVATUM (Neumann, 1909, b). 



Plate 25. 



This species was described from 52 specimens collected in the 

 South Atlantic Ocean (Deutsche Siid-polar Expedition). It is 

 specially characterized by the egg-shaped or almost spherical colony, 

 and by the long tubelike buccal processes standing out here and 

 there from the surface of the test. The species is quite distinct from 

 all other known Pyrosornas; its characters are well defined, and there 

 appears to be no intergrading of this with other forms. The length 

 of the colony is given as 1 to 5? centimeters. The processes of the 

 test show some resemblance to those in P. atlanticum atlanticum, 

 but this resemblance is probably only superficial. The surface of 



