1908] Davis. — Life-history of DolicJioglossus. 191 



My observations aiiree substantially with the first part of ):his 

 statement, but not with that part referring to irregularity of 

 hatching. In his second paper (Bateson '85, p. 2) he says: 

 "From further observation it seems probable that this period 

 (Stage D) assigned as the time of hatching is too early; for 

 embryos kept in aquaria do not break the membranous shell be- 

 fore Stage G is reached. Probably, therefore, the larvae found 

 swimming in Stage D had escaped owing to an artificial rupture 

 of the shell during the process by which they w^ere found,^ an 

 account of which is given in an appendix." 



I am inclined to think that the presence of late unhatched 

 larvae is also abnormal and exceptional. As will be described 

 in detail later, the stages of normal larvae immediately preceding 

 hatching is one of great activity within the egg-shell. It might 

 be supposed that in exceptional cases larvae would not be suffi- 

 ciently active to effect an opening. In such cases there is no 

 apparent reason why the larvae should not pass through the later 

 stages of development within the egg-shell; no instance of this 

 kind, however, has come within my observation. 



The second or climactic period includes the period of active 

 swinnning. 



The third or metamorphic period includes two phases: one 

 of rapid crawling, mainly by means of the ciliary band, and one 

 of slow crawling, by means of proboscis and body cilia. 



These periods are not absolutely distinct in the sense of being 

 delimited from one another. Period II gradually merges into 

 period III by the active swimming cycles, as will subsequently be 

 described, becoming less frequent. The same is true of the two 

 phases of period III, for the movements by means of proboscis 

 and small cilia are gradually substituted for those made by the 

 ciliary band. The three periods above described will hereafter 

 be referred to by their numbers : I, II, III. 



' The essential steps of this process are as follo'*\s: (a) Shake up mud in 

 vessel, avoiding rotary (Mirrents; (b) put in this, minped balanoglossus and 

 allow to settle a few "minutes; (r) siphon off lighter particles in suspension 

 until balanoglossus fragments are reached; ((?) draw this portion off and in 

 it will be found the endjryos. 



