402 ZOOLOGY. 



pears within its body. We will now briefly trace the devel- 

 opment of the chain-salpa, condensing Brooks's statement. 

 The aforesaid tube is at first simply a cup-like protrusion of 

 the outer tunic into the cellulose test which now surrounds 

 the embryo ; the cavity of the cup is an offshoot from the 

 sinus-system, the blood passing in and out of it. A small 

 bud-like protrusion now appears upon the surface of the per- 

 icardium, and lengthens to form a long rod or stolon, ex- 

 tending across the sinus and projecting into the cavity of the 

 cup. At about this period a long, club-shaped mass of pro- 

 toplasm appears within each of the sinus-chambers of the 

 tube, and soon after the outer wall is constricted at regular 

 intervals, each segment being destined to form the outer tu- 

 nics of the chain-salpae, the constrictions indicating the 

 bodies of the latter. 



By the deepening of these constrictions, each of the 

 sinus-chambers, which are diverticula from the body-cav- 

 ity of the solitary Salpa, becomes divided up to form the 

 body-cavities of the Salpas on one side of the chain. From 

 the central tube of the stolon arises a row of buds on each 

 side, which become the branchial and digestive organs of the 

 Salpae on each side of the chain ; while a similar double row, 

 upon the other edge, gives rise to the ganglia. The club- 

 shaped organs within the sinus-chambers become divided up 

 into single rows of eggs, one of which passes into the body- 

 cavity of each chain-salpa at a very early period of develop- 

 ment. 



Thus, as Huxley states, budding occurs, not from the outer 

 wall alone, as in Hydroids and Polyzoa, "but, from "the first, 

 several components, derived from as many distinct parts of 

 the parental organism, are distinguishable in it, and each com- 

 ponent is the source of certain parts of the new being, and 

 of these only. " Prof. Brooks adds that while these- changes 

 are going on the constrictions on the surface deepen, the 

 wall protruding from them, and each is soon seen to mark 

 off, on each side of the stolon, the body of a young Salpa, 

 which soon becomes visible to the naked eye. They do not 

 increase in size gradually from one end of the stolon or tube 

 to the other, but develop in sets of from thirty to fifty each. 



