A TAXONOMIC STUDY ON PYROSOMA METCALF AND HOPKINS. 243 



definite masses of reddish pigment cells lying on the esophagus and 

 on the intestine, and occasionally some on the surface of the testis. 

 These latter are very much in evidence in the yellowish colonies of 

 P. at/iiiificiini giganteum, where they can sometimes be seen with the 

 unaided eye. It is this pigment which is thought to give the sand- 

 yellow color to so many Pyrosoma colonies. The specimens of all 

 forms of the species ailantlcum collected by the Albatross in the 

 Pacific are for the most part colorless or white. 



The cloacal chamber is quite variable in form and size. It rarely 

 exceeds half the length of the branchial sac; as typically developed 

 it is much shorter than this. Its aperture is small. In good sized 

 colonies young zooids, that is, independent buds, have long, neck-like 

 oral and atrial siphons which seem to shorten somewhat (relatively) 

 as these zooids mature. When the cloaca is long it is usually narrow, 

 and its pair of muscles correspondingly short; when short it may 

 be quite broad. 



Gonads. The testis is a fairly compact, spherical body, consisting 

 of 12 to 15 lobes. It protrudes strongly beyond the ventral body 

 contour. Many of the well formed zooids of the colony are protan- 

 drous. According to our observations, in the majority of buds the 

 egg ripens first, while in others the two come to maturity at about 

 the same time. In other words, there is a strong tendency for a 

 protandrous relation to establish itself in many individuals in the 

 colony, probably, as Neumann thinks, as a result of the rapid rate 

 at which budding occurs. This formation of buds by the early 

 formed zodids, increasing the size of the colony, diverts nutriment 

 from the growing germ cells, and the egg, which requires abundant 

 nutrition for its growth, has its development retarded. The testis 

 is thus enabled through its slow but steady growth to reach matu- 

 rity first. The egg when fully grown is larger than the testis by 

 one or two diameters. When it finally becomes detached from its 

 position in the ovary, it completes its brood development in the 

 cloaca of the zooid — not in one of the peribronchial pouches. 



P. atlanticum atlanticum is one of the most abundant forms of Pyro- 

 soma known. It is certainly the predominant form in the Pacific 

 Ocean, where it is of common occurrence on both the east and west 

 sides (California coast, vicinity of Philippine Islands, and the coast 

 of Japan), and the Pacific Ocean is probably more prolific in Pyro- 

 somas than is any other one of the great oceans. The largest number 

 of species is reported from the Indian Ocean, but in number of colo- 

 nies the collections from the Pacific probably surpass even those 

 from the Indian Ocean. Its occurrence in the Atlantic Ocean as a 

 form woll demarcated from giganteum is a little doubtful. We find 

 numerous specimens in the Atlantic Ocean, showing various inter- 

 mediate conditions, but none which could be considered characteristic 



