TYPE PROTOCHORDATA. 637 



going enlargement, so that it serves eventually as a loconiotor 

 individual for the entire aggregation of individuals. 



With regard to the median buds differences of opinion 

 occur. Certain of them, or according to one authority all, 

 being set free, develop into forms possessing but eight muscle- 

 bands, no otocyst or dorsal process, but having a ventral 

 median process upon which buds are found. It is in regard 

 to the origin of these buds that the difference of opinion 

 exists. According to one view they are produced from the 

 ventral process which is regarded as a stolon and represent a 

 third generation, while according to the other view they are 

 certain members of the median row of the second generation, 

 the forms bearing them being as it were their sisters and 

 serving as nurses for them. Whatever may be their origin, 

 however, the buds eventually are transformed into sexual 

 individuals (Fig. 291, B) with which the life-cycle was com- 

 menced. The two views as to the cycle in Ddiolum may be 

 schematically represented thus : 



/ Nutritive individuals 



Ovum non-sexual form^Nurses Sexual forms Ova 



^-Nutritive individuals 



Nutritive individuals 



x 

 Ovum = non-sexual former 



X^-Sexual forms -- Ova 



x Nutritive individuals 



Mention should be made of the genus Octacnemus, a deap-sea form be- 

 longing to this order which is apparently attached by a pedicle to foreign 

 bodies. The body proper is flattened and disklike, its margins being pro- 

 longed into eight tapering processes. The mouth lies on the surface of the 

 disk and leads into a shallow branchial sac. The atrium is comparatively 

 large, and the intestine and viscera are, as in Salpa, massed together in 

 the form of a nucleus. Nothing is as yet known as to the life-history of 

 this form. 



Affinities of the Urodiorda. There seems little room for doubt but 

 that the Urochorda are related to AmpTiioxus. The two groups pre- 

 sent too many common structural features to allow of their being re- 

 garded as distinct types, but at the same time it is noticeable that the 

 relationship is through the larval Tunicates rather than through the 

 adults. These latter are degenerated forms, the entire group forming a 

 degenerate offset from the main line of evolution represented by the Proto- 

 chordata and leading to the Vertebrata. The early stages of development 



