474 



SEMEN. 



may be most readily traced among birds, the 

 increase of size of the testicles being very 

 striking with them at the period of copula- 

 tion, as proved by the researches of Hunter, 

 as quoted by Owen*, to which we may add 

 our own, which likewise have been instituted 

 with the sparrow. 



During the winter the testicles only pos- 

 sess a very small size. In a specimen which 

 we examined in the middle of January, they 

 scarcely measured a millimeter. Both tes- 

 ticles were equally developed, had a globular 

 shape, and weighed together (in a fresh state) 

 about 3 milligrammes. The vasa deferentia, 

 which we were only enabled to discover after 

 a very accurate examination, appeared in the 

 shape of a couple of thin and almost solid 

 strings. Henceforward the testicles and sper- 

 matic ducts begin to grow, although at first 

 but very slowly. The increase of the testicles 

 does not however extend itself in all directions. 

 It is limited principally to the longitudinal 

 diameter, thus causing the subsequent kidney 

 form of these parts. Towards the end of the 

 month of January they reach the length of 

 about 1 Mm., whilst the transverse diameter 

 is not materially changed ; weight of both tes- 

 ticles =4 Mgrs. In the middle of February 

 the length reached about 2 Mm., the width 

 1-g-, the weight 6 Mgrs. By the end of the 

 month the organ enlarges itself to a body of 

 2 Mm. in length, If Mm. in width, with a 

 weight of 8 Mgrs. At the commencement of the 

 next month the testicles measured 2| Mm. in 

 length, 2 Mm. in width. They had a weight 

 of 15 Mgrs., which increased at the middle of 

 the same month to 48 Mgrs., the length simul- 

 taneously increasing to 3^ Mm., the width to 2-f. 

 The subsequent developement of the testicles 

 is much more rapid and extensive. At the 

 commencement of April we found them to be 

 of a considerable size, with a longitudinal 

 diameter of 8 Mm., a width of almost 7 Mm. 

 The weight, we are sorry to say, we did not 

 note down. The microscopical analysis now 

 for the first time exhibited to our view 

 spermatozoa in the different stages of de- 

 velopement. The former stages of develope- 

 ment had not been capable of producing such 

 formations, 



The testicles obtain their perfect develope- 

 ment towards the end of this month (April), 

 when they measure 10 Mm. in length, with a 

 width of 8 Mm., and a weight of nearly 

 f Gramme (0.575 Gramme.). 



The researches which we have now com- 

 municated are of course only of an average 

 value or validity, and cannot be applied to all 

 individual cases. Deviations from them are 

 therefore by no means rare. Individual spe- 

 cimens exhibit either a very premature or 

 a very late developement. Thus we met with, 

 for instance, as early as the middle of 

 January, specimens, the testicles of which had 

 a length of 2 Mm., a width of 1 , and a 

 weight of 6 Mgrs., such occurring usually only 

 four weeks afterwards. Towards the end of 



* Vol. I. p. 354. art. AVES. 



the same month the testicles of another indi- 

 vidual measured a length of 2, a width of 

 2 Mm. As an opposite instance, we may 

 mention that we found at the end of the month 

 of February, in the testicles of a sparrow, a 

 length of 1 J- Mm., a width of 1 Mm. 



Form and history of developement of the sper- 

 matozoa. The first thing that strikes the 

 observer, on entering into a microscopical 

 research of the semen of a great number of ani- 

 mals, is the difference of the shape of the sper- 

 matozoa. The specific shape of these elements 

 generally corresponds with the individual 

 classes, genera, and species, and this so dis- 

 tinctly, that one may often safely venture to 

 infer from it the systematic position and the 

 name of the animals investigated. We will not, 

 however, venture to determine whether this 

 variety of the shape is connected with the rich 

 variety of animal formations, or whether the 

 specific shape of the spermatozoa has a de- 

 termining influence upon the developement 

 of the germ into a certain specific form. 

 Such a conjecture, however, would certainly 

 not be supported by the circumstance that a 

 corresponding shape of the spermatozoa is 

 frequently met with in animals very far re- 

 moved, indeed quite different, from each other. 

 The variety of form in the spermatic elements 

 is the more striking, because the female ge- 

 nerative elements, throughout the animal 

 creation, are distinguished by a uniform de- 

 velopement. 



Most of the spermatozoa have a slender, 

 linear body, either filiform throughout, or 

 swollen and enlarged at one end, which 

 for convenience we designate the anterior 

 end. This swollen extremity is differently 

 developed, and frequently grown into a 

 peculiar independent part, as, for instance, 

 into a head or body, from which the other 

 thin and longer part is extended as a whip- 

 like tail. Various other forms of the sper- 

 matozoa cannot, however, well be reduced 

 to this type, or at least only by the assump- 

 tion that the filiform body is abridged in its 

 longitudinal axis, to compensate for which 

 it afterwards increases much in width and 

 thickness. Hence the short dense thick 

 corpuscles of a different shape, which are 

 occasionally found in the genuine semen in- 

 stead of the filiform spermatozoa. The size 

 of the spermatozoa, like the size of all the 

 elementary constituents of the animal body, is 

 only very slight. It is only in a few cases that 

 it exceeds the length of aline, a much shorter 

 dimension being however much more general. 



Let us now trace the different histological 

 formations of the semen, according to form 

 and connexion in the principal groups in the 

 animal creation. 



MAN. In man (in which the sperma- 

 tozoa (fig. 323.) are composed of head and 

 tail), as indeed generally in the whole division 

 of the Vertebrata, the size * does not often 

 amount to more than /", at the outside /". 



* We always refer in our measurements to Pari- 

 sian lines ; a miUirn. = 0.443 of a Paris line. 



