OF inE HYDATIJJf^A. 677 



FAMILY v.— HYDATINJEA. 



Illoricated Rotifera, having the ciliated wreath divided into several lobes 

 or subdivisions. 



In many of the genera distinct striated muscles of the voluntary type exist, 

 effecting the various movements and altering the form of the body. The 

 nutritive system usually consists of a simple conical ahmentary canal without 

 a distinctly separated stomach (Coelogastrica) ; but a pyloric constriction exists 

 in Hydatina, some Notommatce, and other forms. Notommata davulata and 

 Diglena lacustris have special caeca appended to their stomachs. Yaiiously 

 modified cellular appendages, supposed to be glandular, exist in aU the genera. 

 The ovarium is mostly ovate and only evolves a few ova at a time. In 

 Notommata Myrmeho, N. davulata, and Diglena lacustris it is very long. In 

 all it communicates with the cloaca, by an oviduct of varying length. The 

 ova vary considerably, and belong to two distinct types, respectively termed 

 the summer and winter ova. The former have a smooth shell, and are gene- 

 rally regarded as mere unimpregnated gemmae, like those of Aphides amongst 

 insects. The latter are hard, and often spinous, in which form M. Tarpin 

 regards them as constituting the genera Bursella and Erithrinella (?) amongst 

 plants. It is amongst the members of this group that many of the interesting 

 researches of Daliymple and others have been made, demonstrating the exist- 

 ence of dioecious animals. Amongst the Rotifera the male animals of Hydatina 

 and Asplandina are distinct from the females. They are generally character- 

 ized by their smaller size and by the absence of digestive organs — indicating 

 a brief existence, during which the vis vitce derived from the ovum suffices to 

 sustain the animals in ful filing their several functions. According to Cohn, 

 this absence of an alimentary canal in the males does not characterize the 

 male of Notommata parasitica (XXXIX. 8) ; but this is so exceptional to 

 aU other allied discoveries as to suggest a doubt of its correctness : at 

 the same time, we have scarcely crossed the threshold of this inquiry, and 

 want the materials for general conclusions. Water-vascular canals, variously 

 modified, exist in most of the Hydatinsea. The frequent association of the 

 red " eye-spots" with a subjacent organ, supposed to be a cerebral ganglion, 

 suggests sensational functions ; but no true nerves occur. 



Some species of Synchceta are said to evolve light and contribute to the 

 phosphorescence of the sea. Hydatina senta, Diglena catellina, and Triarthra 

 are sometimes so numerous as to render the pools in which they reside milky 

 and turbid. 



Ehrenberg's classification of this family is given at p. 478, Section Soro- 

 trocha, Division Polytrocha. 



The first genus (EXTEROPLEA), established to receive E. hyalina, has 

 been shown by Leydig to have no existence, as the above animalcule proves 

 to be the male of Hydatina senta. 



Genus HYDATINA (XXXII. 394 ; XL. 1, 2).— Eyes absent. The female 

 has two jaws, consisting of several teeth and a forked foot. Locomotion is 

 effected by the compound wheel organ and the pincer-like foot, acted upon 

 by complex internal muscles. In Hydatina senta the sexes are distinct, the 

 Eftiteroplea hyalina being the male form. 



Hydatina senta ( Vorticella senta, M.) 

 (xxxii. 394 ; xl. 1).— Body of the female 

 conical, hyaline ; rotary organ consisting 

 of a simple external wreath of cilia sm-- 

 rounding the truncate anterior extremity 

 of the Dodv, and enclosinof at the back 



part of the head an interrupted row of 

 tufts of cilia supported on small hemi- 

 spherical projections, — the cilia of the 

 latter broader and longer than those of 

 the external row. Within these is a 

 third uninterrupted line of cilia. Neck 



