No. 501] 



NOTES AND LITERATURE 



625 



Bateson, develops directly also, it is hardly necessary to mention. 

 Since the two species arc much alike in most other respects as 

 well, the desirability nf examining the development of the Pacific 

 species was obvious. The report before us is confessedly incom- 

 plete so. far as the entire developmental history is concerned. 

 In some of the phases treated it is, however, measurably full and 

 apparently conclusive. The point of most importance perhaps 

 as developmental problems are now estimated, pertains to the 

 origin of the body cavities. Bateson seemed to find these to 

 arise as five diverticula from the archenteron, viz., one anterior 

 which produces the cavity of the pre-oral lobe, or in the final 

 state the proboscis, a pair immediately behind this producing 

 the cavities of the collar region of the adult, and behind these 

 another pair wdiich produces the cavities of the rest of the 

 animal, i. e.) of the thoracic and abdominal portions. 



Davis finds a radically different course of things. In the 

 embryo studied by him a single anterior pouch arises as in D. 

 Kowalevskii, but instead of the two pairs coming directly from 

 the archenteron, the one anterior pouch sends back lateral 

 pockets between the ectoderm and endoderm, and from these 

 there is constricted off first a pair of cavities which correspond 

 to the future collar, and then in turn from the posterior end of 

 this collar pair, a second pair, presumably representing the 

 future cavities of the thoracic-abdominal region of the adult, is 

 cut off. Since Davis's results rest upon the examination of a 

 large number of embryos (about one hundred and fifty series 

 of sections, he tells us) , preserved in a variety of ways and cut 

 in various directions, it seems they must be accepted, and so the 

 conclusion reached that either Bateson 's interpretation of his 

 sections was seriously erroneous, or that these two species so 

 closely alike in most respects are unlike in this supposedly fun- 

 damental point. Davis strongly inclines to the first view and 

 presents cogent reasons for his inclination based on a critical 

 study of Bateson 's text and figures. 



The bearing of this finding on the problem of the relationship 

 between Balanoglossus and Amphioxus is clear. The supposed 

 similarity of origin of the body cavities has been taken as a 

 leading proof of genetic kinship between the two animals. Davis 

 does not fail to point out that his observations justify the doubts 

 of the correctness of Bateson 's conclusions entertained by both 

 Spengel and Morgan and drawn from their studies of tornaria. 



