229 



N'OTE ON THE CONSTRUCTION OP THE LORICA IN THE GeNUS 



Brachionus. 



By Surgeon V. Gunson Thorpe, R.N., F.R.M.S. 

 (H.M.S. "Peacock," China). 



After careful examination of many of the known species of 

 Brachioni, as well as many new species and varieties found in 

 tropical countries, I have come to the conclusion that the so- 

 called dorsal surface of the lorica in reality consists of two 

 plates, instead of the one antero-posteriorly curved plate as 

 generally received. This doctrine, it seems to me, has been 

 strengthened by many new discoveries since the valuable 

 monograph on the "Rotifera" was first issued. My proposition, 

 therefore, is this, that the lorica of a Brachionas be in future 

 described as consisting of a ventral, a dorsal, and a hasal plate, 

 the latter two constituting what is now known as the dorsal 

 surface. I consider that I am supported in this view by the 

 following considerations : The so-called dorsal surface of the 

 lorica in B. ruhens (Fig. 1), B. urceolaris, and other species is 

 divided in the majority of individuals by a very sharp line of 

 demarcation at the junction of the upper two-thirds wdth the 

 lower one- third, where the lorica curves to join the ventral 

 surface posteriorly. No doubt there are cases in which the 

 division of the dorsal surface into a dorsal and basal plate is not 

 so well defined (Fig. 3), but I think that these cases are in a 

 minority. In B. militaris (Fig. 2) and also in B. quadrahis one 

 sees the basal plate extremely well defined. But the argu- 

 ment is still further strengthened by the fact that I had the 

 good fortune to discover in 1890, at the Cape of Good Hope, a 

 Brachionus {B. ftirculatus), in which the dorsal plate was pro- 

 longed posteriorly (Fig. 6) so as to form a wedge-shaped space 

 between the lower portion of the dorsal plate and the basal 

 plate, in which space parasitic infusoria took up their abode.* 

 Since then I have come across in Ceylon and China transitional 



* " Journ. R. Micros. Soc.," 1891, p. 302. 



