214 University of California Publications in Zoology. [ y L - 4 



pouches, viz., one anterior unpaired pouch and two pairs of 

 lateral pouches. Of these, the first divides to form the two head 

 cavities ; the anterior pair give rise to the first pair of myotomes, 

 and in addition to two long canals extending back ventrally ; the 

 posterior pair are gradually separated from the gut, and pari 

 passu divided into a series of myotomes. The whole process of 

 mesoderm formation is therefore referable to the type found in 

 Balanoglossus, the main difference being that the pouch corre- 

 sponding to the trunk coelom of Balanoglossus becomes seg- 

 mented." Pp. 606-607. 



He reproduces, though somewhat modified, the diagram which 

 Bateson '84 (fig. 40) used to illustrate the body cavities of Balan- 

 oglossus. When seen side by side, Bateson J s diagram of the body 

 cavities of Balanoglossus and MacBride 's diagram of the body 

 cavities of Amphioxus are strikingly similar. If one were to 

 judge by these the homology of the cavities of the two animals 

 would seem to be well established. 



Recently MacBride 's work has been questioned. Cerfontaine, 

 '05, says of MacBride 's contention that in Amphioxus the meso- 

 blast occurs in five diverticula : ' '.Je dirai des a present, que, 

 dan mes nombreuses preparations je n'ai jamais vu, quoi que ce 

 soit, qui puisse avoir des rapports avec une semblable evolution 

 du mesoblaste chez 1'Amphioxus, et je dois encore une fois repeter 

 que certaines figures, qui accompagnent le memoire de MacBride 

 denotent, tvidemment, une mauvaise conservation du material." 

 p. 364. "L'ebauche du mesoblaste, existe sur tout le pourtour 

 1'ebauche notochorde. Cette ebauche du mesoblaste, au moment 

 de I'achevement des phenomenes de gastrulation, presente, avec 

 1'orifice d'invagination des rapports tels, qu'on doit distinguer 

 chez I'Amphioxus, mangre 1'absence des cellules polaires de 

 Hatschek, un mesoblaste gastral et un mesoblaste prostomial. " 

 p. 389. With such a disagreement as to the origin of the meso- 

 derm in Amphioxus it would be difficult to homologize the body 

 cavities of this animal and those of Balanoglossus even if Bate- 

 son's account of the latter be accepted. But the difficulty grows 

 into an impossibility if I have made my case as to the origin of the 

 cavities of D. pusillus and as to the improbability that they arise 

 differently in D. kowaleveskii from what they do in D. pusillus. 



