48 



LOWER INVERTEBRATES. 



tilis, whose acinetiform embryo it was once regarded. Its stalk is long, the body ovate, 

 with the upper border divided into four tentacle-bearing lobes in the adult; in the 

 young there is but one lobe ; this gives place to two, and finally to the full number. 

 According to ClaparSde and Lachmann, two sorts of embryos, large and smaU, are de- 

 veloped ; the former .enclose a portion only of the nucleus of the parent. According to 

 Btltschli they are liberated through a specially developed orifice ; the other forms are 



produced by the sub-division of the nucleus. 

 In both cases, at. the time of liberation, the 

 embryos are ciliated like the peritrichous In- 

 fusoria, with an equatorial girdle and anterior 

 tuft. In Hemiophrya gemmipara (Fig. 47), 

 we have a remarkable Acinetan. There are 

 two sorts of tentacles, viz., a few, centrally 

 placed, of the usual suctorial type, and a 

 larger number of prehensile ones around the 

 border. When the latter are seen under a 

 high magnification the surface is seen to be 

 not smooth, but nodula,r, the component par- 

 ticles of externally developed granular pro- 

 toplasm being usually disposed in a spiral 

 manner around the central axis. The production of embryos by gemmation has been 

 referi'ed to on a previous page. The genus Acineta has many representatives inhabiting 

 both salt and fresh water. An interesting species is found in large numbers on the sur- 

 face of a Mysis taken in the Great Lakes. 



Fig. 47. 



- Hemiophrya gemmipara, magnified 

 150 times. 



SuB-OkDER II. — ACTINARIA. 



This sub-order includes a few forms in which the tentacles are filiform and prehen- 

 sile. They are inhabitants of salt-water, and, like their nearest relatives, are mostly 

 commensal upon aquatic animals. 



D. S. Kellicott. 



