SALPIDA. 



53 



stolon are divided by the segmentation except the outer ectoderm, the 

 blood-sinuses, and the endodermal tube. These are continuous from end 

 to end of the stolon, being found in the narrow stalks which connect the 

 buds as well as in the buds themselves (Fig. 45). The stolon has therefore 

 now the form of a chain of developing zooids connected together, the dorsal 

 surface of one to the ventral surface of the next, by short narrow stalks. 

 Meanwhile, the proximal part of the stolon, between the zooids and the 

 parent, has been growing, and undergoing a similar process of segmenta- 

 tion into a group of buds. This process is repeated, so that eventually 

 a chain is formed consisting of groups of from 50 to 100 zooids. The indi- 

 viduals of each group are of the same age, but the groups next the parent 

 consist of younger individuals than the distal and earlier formed groups. 

 As development proceeds a change in the attachment of the zooids is 

 effected. At first they are arranged in a single row, the intermediate con- 

 stricted part of the stolon passing from the ventral surface of one to the 

 dorsal surface of the next (Fig. 45). Soon, as a result of growth, by which 

 the relations of the parts are changed, and of rotation, they become 

 arranged in a double row, the zooids of one row alternating with those of 



FIG. 45. Diagram representing a stolon of Salpa as it would appear if no secondary shifting 

 of the individuals were to take place (after Brooks, from Korschelt and Heider). P solitary 

 form (parent) ; /, //, ///, first, second and third group of individuals (the number shown 

 in each group is much smaller than actually occurs) ; b, b", b'" pharynx ; c", c'" 

 atrium ; d digestive canal ; ee ectoderm ; el elaeoblast ; en endoderm of the connecting 

 stalks ; es endostyle ; g gill ; h heart ; ganglion ; o", o'" ovary. 



the other. Later the intermediate constricted part of the stolon, which joins 

 them, atrophies and the zooids remain adherent by processes of the body- 

 wall and test, which have become developed for the purpose. When this 

 happens the zooids of the group affected become detached from the proxi- 

 mal part of the stolon and form a free-swimming chain of sexual individuals 

 all of the same age and connected by processes of the body wall and test. 



The sexual zooids when full grown are of about the same size as the 

 asexual. The ovaries are formed early and the ova are fertilised before 

 the testes are developed. Fertilisation therefore must be effected by 

 spermatozoa produced by another chain. 



Cyclosalpa Blainville, digestive tube running antero-posteriorly and not 

 coiled up to form a nucleus ; the chain-forms are attached together in a 

 circle. G. pinnata Forsk., with linear bands, C. affinis Cham., without 

 linear bands. Salpa Forskal, digestive tube coiled up in the nucleus, one 

 embryo, chain as elongated band, S. africana-maxima Forsk. Thalia 



