382 GENEEAL HISTORY OF THE LNTUSORIA. 



like aggregation of rounded cells. The posterior portion of the ovary exhibits 

 ova, having a germinal vesicle and spot surrounded by a fine granular yelk- 

 mass ; and one or two ova are frequently seen separated, having a delicate 

 colourless shell developed around them. The diameter of the largest ova 

 equals ^^Q-th. The mature eggs lie close to the testes. Besides this distinct 

 male organ, two groups of sjpermatozoid-ceMs seem present, lying apparently 

 free in the loose parenchyma, and apparently without any investing membrane 

 or envelope. As to their affinity, Schultze makes no doubt that they are 

 Vermes, and belong to the group of Turbellaria, considered as a division of 

 the Cestoidea. Among Turbellaria they are best placed with the Arhynchia, 

 including Mkrostomum and DlnopliUus. They resemble Nematoidea and 

 Anquilhdce in the form of the intestinal canal, but are unlike these in their 

 figure, their ciliated integument, and their hermaphrodite structiu-e. 



The IcJithi/dina are inhabitants of fresh water, l\ving among aquatic plants. 

 They have a sluggish, creeping gliding movement, resembling that of most 

 Turbellaria. 



FAMILY II.— NOCTILUCIDA. 



(Plate XXXI. 32-39). 



This small but remarkable subsection is represented by only one animal, 

 the Noctduca mdiayns, which has attracted much attention as one of the 

 sources of the phosphorescence of the sea. By several recent authors it 

 has been treated as a near aUy of the Cihata, although it must be confessed 

 to have few outward indications of such a relationship, and, in oui' estima- 

 tion, is a representative of quite a different and independent group of 

 animals. At first sight, a Noctduca appears a round gelatinous corpuscle 

 having a depression or groove at one part, surmounted by a filamentary pro- 

 cess or tentacle. Compared with the Ciliated Protozoa, it is of gigantic pro- 

 portions, attaining -gL-th of an inch in diameter. On closer examination it is 

 found to have an integument of two layers : the outer smooth and reticular, 

 structureless, and of considerable density ; the inner a delicate, granular, 

 gelatinous membrane, which Dr. Webb {J. M. S. 1855, p. 103) describes to be 

 in union at all points with the whole system of reticulations spreading from 

 the central organs, — a fact rendered e\ident by the action of indigo and the 

 primary changes consequent on death. '' The internal fibrous reticulations 

 gradually contracted, drawing the ' vacuoles ' together, and with them the 

 inner membrane. This was detached without rupture, but after a time fell 

 into folds, which so included the other structures as to have the look of a 

 wrinkled tube with a series of pouches ending in a larger membranous sac. 

 The external layer distended by degrees till it suddenly burst. I should 

 mention that a new supi^ly of water had been given before most of these 

 changes happened. I have also been successful in separating the two layers 

 mechanically, by means of pressure, slowly and steadily appKed to the animal 

 under the screw compressor." The external membrane is extended at one 

 point into a tapering process, which acts as a locomotive organ. It springs 

 from the edge of the infundibulum, which is extended backwards into a pha- 

 rynx or gullet. This process or tentacle appears transversely striped, and 

 breaks short ; of the nature of those stripes we know nothing. Dr. Webb 

 believes this process to be tubular, with an orifice on the inner side at 

 its base. " At any rate," he wiites, " 1 have seen the colour, when iodine 

 has been used, proceed towards the distal extremity ; and under the influence 

 of indigo poisoning, the granular matter of which the striation consists has 

 been disarranged, scattered up and down the interior of the organ, and in the 

 end has aggregated together in small globules, without much impairing the 



