DOLIOLIDAE — ASEXUAL REPRODUCTION. 473 



blood-vessels separated by ;i partition-wall of connective tissue. The 

 transverse section of this outgrowth, indeed, strikingly recalls 

 sections through the stolon of certain Ascidians, although it must 

 be noted that, in these latter, the partition-wall is formed by an 

 entodermal lamella (epicardial lamella) of which nothing can be seen 

 in Doliolum. 



The buds which develop from the dorsal outgrowth as lateral and 

 median buds (Fig. :243, /, m) do not arise independently from this 

 structure. Grobben conjectured that they were all abstricted from 

 a " primitive bud " found at the base of the stolon. Ulianin, on the 

 other hand, observed that the parts which become abstricted from the 

 ventral stolon are capable of wandering along the surface of the body 

 of the parent, and in this way reach the dorsal outgrowth (u, u'). 

 These wandering cell-masses are the primitive buds, from which the 

 lateral and median buds of the dorsal outgrowth arise by constriction. 

 The primitive buds that first reach the dorsal outgrowth remain at 

 its base and, through fission, produce buds which become arranged 

 along each side of the stolon, developing into the lateral buds or 

 gastrozooids (/) : consequently the buds towards the distal end of the 

 row are more highly developed than those near its base. Those 

 primitive buds which reach the dorsal outgrowth later are distributed 

 along the whole of the middle dorsal line (""), and by gemmation give 

 rise to the median buds or phorozooids (m). These buds are arranged 

 in groups alternating on either side of the row of primitive buds (><"). 

 The I tin Is of each group develop unequally, but here also there is 

 an advance in development towards the distal end of the stolon. 



According to Uljanin, the ventral stolon is thus the only prolifer- 

 ating stolon of the " nurse " generation ; the dorsal outgrowth cannot 

 be regarded as a true proliferating stolon, but is merely a body-process 

 serving for the nourishment of the buds attached to it, which can be 

 traced hack to the mantle-vessels of the Ascidians. 



The Doliolidae thus show an early detachment of the buds from the 

 proliferating stolon such as takes place in the Distomidae (pp. 456 and 463), in 

 which family also the detached buds are able to multiply further through 

 fission. The wandering of the primitive buds and the development of their 

 descendants in their secondary position in the Doliolidae are very remarkable. 

 The statements made mi this subject have been confirmed for Doliolum by 

 Baerois (No. 77), and similar processes have been observed in Anchinia and 

 Dolchinia, so that little room is left for doubt on this point. According to 

 Uljanin, the buds are able to move by means of pseudopodia-like processes 

 of their ectoderm-cells. According to Barrois, on the contrary, there are, 

 on each side of the ventral stolon of Doliolum, large amoeboid cells, arranged 



