410 



ORGANS OF GENERATION. 



The Holothurldse present in the elongated 

 form of their bodies an evident approximation 

 to the annul ose type of structure, and a propor- 

 tionate concentration of the generative system ; 

 in these we find but one ovary floating loosely 

 in the visceral cavity, and composed of numerous 

 very long cceca, which terminate by a single 

 orifice placed on the median line, near the oral 

 extremity of the animal.* The eggs when dis- 

 charged are connected into masses composed 

 of long strings of ova, but the mode of their 

 development is but little known. 



Although from the relations of the Mollus- 

 cous division of the animal kingdom we might 

 infer that a more elevated type of structure 

 would characterize their organs of reproduction, 

 the present state of our knowledge of the 

 anatomy of these creatures compels us to arrange 

 the lowest orders of that extensive class with 

 those tribes which only possess an ovigerous 

 system; for although an androgynous confor- 

 mation is presumed by many to exist in all 

 Bivalves, the presence of any superadded im- 

 pregnating portion has not yet been pointed 

 out, and even the course of the ova in their 

 passage from the ovarian cavity remains a mat- 

 ter of speculation. In the Conchiferous order, 

 from causes sufficiently obvious when we con- 

 sider the peculiar structure of the animals 

 which compose it, the full development of 

 their numerous ova could not be accom- 

 plished in the ovary itself, which occupies a 

 large portion of the body, as any material in- 

 crease of bulk produced from this cause would 

 materially interfere with the closing of the 

 shell; at an early period, therefore, the ova 

 are transferred from the nidus in which they 

 were formed to the branchial fringes, between 

 the laminae of which they perfect their growth, 

 and are fully exposed to the influence of the 

 element around them. Oken traced a canal 

 through which he supposed the ova to be con- 

 veyed directly from the ovaria to the gills ;f 

 but notwithstanding his observations Carus 

 contends J that the eggs pass into the stomach 

 through one of the openings hitherto considered 

 as belonging exclusively to the biliary ducts, 

 whence they are evacuated through the mouth 

 and conveyed into the openings of the gills 

 by the water which flows between the pallial 

 laminae from before backwards, and ultimately 

 escape by two canals which open below the anal 

 tubes. 



In the Tunicata, and also in those forms of 

 the Gasteropodous Mollusca which most nearly 

 approximate the Conchifera in the details of 

 their organization, the ovary is imbedded in 

 the substance of the liver, and the ova are dis- 



* Here, also, Blainville conjectures that there is 

 a supplementary impregnating portion, but it is 

 evident that in a treatise like the present it 

 would be worse than useless to recapitulate the 

 surmises of authors upon subjects only capable of 

 solution by positive demonstration, and we shall 

 therefore endeavour rather to adhere strictly to the 

 narration of what is clearly established by observa- 

 tion, than to indicate what theory or analogy would 

 lead us to suspect. 



f Goetting, gel. Anzeigen, 180(5. 



J Introduct. to Comp. Anat. 



charged through a simple duct, unprovided 

 with any appendage which can be looked upon 

 as a male apparatus. It is true, indeed, that 

 in all these cases the walls of the oviduct may 

 themselves furnish a fertilizing fluid, and by 

 many physiologists they are supposed thus to 

 supply the want of male parts ; such an hypo- 

 thesis, however, is, to say the least of it, 

 entirely gratuitous ; but as it is more our busi- 

 ness to trace the development of organs than 

 the modes in which their deficiency may be 

 supplied, we are content to leave the question 

 without further discussion in this place. 



SECOND DIVISION. Animals provided with 

 ovigerous organs combined with an addi- 

 tional secreting structure, probably sub- 

 servient to the fertilization of the ova. 



In this type of the generative system it must 

 be obvious that the function attributed to the 

 superadded portion is by no means indubitably 

 substantiated, the opinions of physiologists 

 relating to its office being rather based upon 

 analogical reasoning than supported by direct 

 evidence; and, in fact, some authors deny 

 entirely that a necessity for the impregnation 

 of the ova is more evident in this division than 

 in the last. Nevertheless, although it is im- 

 possible distinctly to prove the identity in 

 function between the appended portion and 

 the testis of higher forms of organization, the 

 evidence afforded from the position which it 

 invariably occupies, and from the considera- 

 tion of the parts connected with generation in 

 difficious animals to which we are insensibly 

 conducted by this species of Hermaphrodism, 

 is sufficiently cogent to warrant our application 

 of the term ovarium to the nidus wherein the 

 ova are produced, and to justify us in designa- 

 ting the accessory organ as a testis or apparatus 

 for impregnation. 



The Taenioid Sterelmintha furnish us with 

 one of the simplest examples of this arrange- 

 ment of the generative organs. In the long 

 and tape-like bodies of these Entozoa each 

 segment, with the exception of the smaller ones 

 near the head, possesses distinct ovigerous and 

 impregnating structures. The female part of 

 the apparatus occupies the centre of the joint, 

 and consists of lateral tubes ramifying from a 

 central canal, which at times may be seen to 

 be full of minute granular ova. From these 

 ovigerous canals a duct issues, which commu- 

 nicates with the lateral pore and receives before 

 its termination two delicate tubes, recognizable 

 under the microscope as dark lines imbedded 

 in the pulpy segment, and which may be pre- 

 sumed to furnish an impregnating secretion. 



In the Rot if era, or wheel-animalcules, the 

 female apparatus consists of two long and 

 comparatively wide sacculi, in which the ova 

 are developed ; these open at the anal orifice, 

 and receive near this point two narrow coeca, 

 which, as in the last case, may secrete a fer- 

 tilizing fluid, serving to impregnate the eggs 

 prior to their expulsion. The ova of these 

 minute creatures, before the escape of the 

 young, are exceedingly beautiful subjects for 

 the microscope, the wheels of the embryo 



