122 HABITUDES AND ATTITUDES 



Another phase of bionomical convergence is that 

 contained in the phenomena of direct and indirect 

 development amongst many invertebrate animals. 

 Direct development is straightforward, gradual, 

 without striking metamorphosis, and must be 

 regarded, in a certain sense, as normal. Works 

 which deal with direct development are apt to 

 become standard and classical ; they give the 

 clue to fundamental homologies and generalisa- 

 tions. The theory of the coelom could hardly 

 have been established upon an indirect course 

 of development ; and on the other hand, the 

 relationship between the Enteropneusta and 

 Echinodermata would not have been recognised 

 so easily from the direct development, although 

 the larva of Asterina gibbosa would doubtless 

 have called for comparison with Bateson's larva 

 of Balanoglossus. 1 The differences between the 

 larvae of certain marine organisms consist in the 

 littoral or stereotropic habit of the direct forms 

 as contrasted with the pelagic or free-swimming 

 (pleotropic) habit of the indirect forms ; and they 

 are anticipated by the size of the egg and the 

 amount of food yolk it contains. A very small 

 egg will develop into a pelagic larva ; a relatively 

 large egg will develop directly into a larva in 



1909, pp. 190, 5 plates. Contains bibliography of Wasmann's 

 numerous contributions to the knowledge of myrmecophily and 

 termitophily. 



1 1 employ this name in the old sense, just as Amphioxus is still 

 extensively used, without trenching upon questions of nomenclature. 



