146 BULLETIN OF THE 



The following summary may be made of the preceding observations : — 



1. The intestine of the bisymmetrical larva is early developed, and 

 later in development becomes atrophied and is lost. 



2. The mouth and oesophagus (1) of the bilateral larva is formed by an 

 invagination of the epiblast while yet the larva is enclosed in its sac and 

 attached to the parent. 



3. The provisional skeleton of the bilateral larva is not always sym- 

 metrical, and sometimes develops on one side. The first-formed rod is 

 not always a trifid calcification. 



4. An umbilical connection exists in all later stages of growth until 

 the pentagonal form is assumed. The relation of the umbilicus to the 

 mouth, stomach, and intestine is described. 



5. The first calcareous plates to form on the abactinal hemisome are 

 five first radials, and a little later a dorsocentral. The radials antedate the 

 terminals. 



6. The first plates to form on the actinal hemisome are the first adam- 

 bulacral. 



7. The second pair of adambulacral plates bear club-shaped spines. 

 These last structures are homologous to the spines of the lateral plates of 

 the arms. 



8. The first ventral plate to form belongs to the first pair of adam- 

 bulacral plates, and not to side plates of the arms. This first ventral, 

 although not belonging to the portion of the arm free from the disk, is 

 homologous to the other ventral arm-plates. 



9. The radial shields originate before a plate called the " underbasal " 

 forms between the dorsocentral and the primary radials, and while there 

 are but two intermediate plates in each of the interradii. 



10. The homology of certain plates of the young Amphiura to the ba- 

 sals, as suggested by Carpenter, is discussed, and doubts advanced whether 

 the individual plates mentioned by him are basals in preference to other 

 interradial plates. 



11. The ambulacral plates do not always originate as trifid spicules, 

 but sometimes first appear as parallel unbranched rods. 



12. A. squamata is infested by a parasitic Crustacean, which, although 

 in adult form closely allied to a Copepod, lays eggs in packets in the 

 host. These ova were found in conditions of cleavage, in a nauplius 

 stage and in intermediate conditions. The adult is also found in the 

 Amphiura. Eggs not attached to adult. 



