112 



EMTOZOA. 



has arrived at maturity, and be diluted with 

 a little pure tepid water and placed in the 

 field of a microscope, a swarm of minute 

 beings resembling tadpoles will be observed 

 moving about with various degrees of velo- 

 city, and in various directions, apparently by 

 means of the inflexions of a filamentary caudal 

 appendage. These are the seminal animalcules, 

 Zoosperms, or Spermatozoa (Jig, 51): and, as 

 it is still undetermined whether they are to be 

 regarded as analogous to the moving filaments 

 of the pollen of plants, or as independent or- 

 ganisms, it has been deemed more convenient 

 to consider them zoographically in the present 

 article as members of the class Entozoa. 



The body to which the tail is attached is 

 of an oval and flattened or compressed form, 

 so that, when viewed sideways, the Zoosperm 

 appears to be a moving filament like a minute 

 Vibrio. It is this compressed form of the 

 body which principally distinguishes the Sper- 

 matozoa or seminal Cercarits^ from the true 

 CercaritR of vegetable infusions, in which the 

 body is ovoid or cylindrical ; the caudal ap- 

 pendage of the Spermatozoa is also propor- 

 tionally longer than in the Cercaria. 



In some species of the latter genus an oral 

 aperture and ocelliform specks of an opake 

 red colour have been obsprved on the anterior 

 part of the body, and they manifest their sen- 

 sibility to light by collecting towards the side 

 of the vessel exposed to that influence. In 

 the Zoosperms, which are developed exclu- 

 sively in the dark recesses of animal bodies, 

 the simplest rudiments of a visual organ would 

 be superfluous; they are, in fact, devoid of 

 ocelli, and even an oral aperture has not yet 

 been detected in these simplest and most mi- 

 nute of Entozoa. In neither the Zoosperms 

 nor the Cercarue has the polygastric struc- 

 ture been determined. On the contrary, some 

 of the non-parasitic species, as the Cercaria 

 LemnaKj are stated to have ' a true alimen- 

 tary canal, not polygastric.' * 



The Spermatozoa are not, however, the only 

 examples of the present order of Protelm'mtha 

 which have their habitat in the interior of living 

 animals ; many of the Entozoa themselves have 

 been observed to be infested by internal para- 

 sites, which are referrible by their external form 

 to the Cercariadee. 



Although no distinct organs of generation 

 have been detected, there is reason to suspect 

 that the Spermatozoa are oviparous : they are 

 also stated to propagate by spontaneous fission ; 

 the separation taking place between the disc of 

 the body and the caudal appendage; each of 

 which develope the part required to form a 

 perfect whole. 



The Zoosperms of each genus of animals 

 present differences of form or proportion, and 

 frequently also differences of relative size as 

 compared to the animal in which they are deve- 

 loped ; thus, in the figures subjoined, which 

 are all magnified in the same degree, the 

 Zoosperm from the Rabbit is nearly as large as 

 that from the Bull, (jig. 51.) 



* Pritchard's Animalcules, p. 184. 



Fig. 51. 



Bull. 



Rabbit. 



Silk-worm Moth. 

 Fig. 52. 



::S& C 



Developinent of Sper 

 matozoa, Bunting. 



They appear to be 

 formed in the seminal 

 secretion under similar 

 laws to those which pre- 

 side over the develop- 

 ment of other Entozoa 

 in the mucous secretion 

 of the Intestines, &c.,but 

 are more constant in their 

 ' existence, and must there- 

 fore be regarded as fulfil- 

 ling some more important 

 office in the economy of 

 the animal in which they 

 exist. 



They are not found in 

 the seminal passages or 

 glands until the full pe- 

 riod of puberty ; and in 

 some cases would seem 

 to be periodically deve- 

 loped. In the Hedgehog 

 and Mole, which exhibit 

 a periodical variation in 

 the size of the testes in a 

 well-marked degree, the 

 Spermatozoa are not ob- 

 servable in those glands 

 during their state of 

 quiescence and partial 

 atrophy. Professor Wag- 

 ner* examined the testes 

 of different Passerine 

 Birds in the winter sea- 

 son, when those bodies 

 are much diminished in 

 size. (See vol.i. p. 354, 

 fig. 183.) They then con- 

 tained only granular sub- 

 stances, without a trace of 

 the Spermatozoa. When 

 the same bodies were ex- 

 amined in spring, they 

 were found to contain 

 spherical granules of dif- 

 ferent sizes and appear- 

 ances, (A, B, fig. 52,) 

 which led to the suppo- 

 sition that they were the 

 ova of the Spermatozoa in 

 different stages of deve- 

 lopment, and capsules 

 containing each a nume- 

 rous group of Sperma- 

 tozoa (C) were also pre- 

 sent; whence it would 

 appear that many of these 

 animalcules were deve- 

 loped from a single ovum. 

 In the semen contained 

 in the vasa deferentia the 

 Spermatozoa (D) were in 

 great numbers, having 

 escaped from their cap- 

 sules ; they exhibit a re- 

 markable rotation on their 



* Mailer's Archiv. 1836, 

 p. 225. 



