478 



SEMEN. 



shape, which gradually passes off into the pos- 

 terior tail-like portion. The body, in most 

 birds prolonged into a cylinder, is distin- 



Fig. 328. 



Spermatozoa of the Cock (Gallus domesticus). 



guished by a greater thickness from the thin 



and filiform tail, which is twice its length (fig- 

 328.). In other instances, how- 



Fig.329. ever, it makes a number of spiral 

 twists, generally four, which make it 

 look like a corkscrew. The anterior 

 end, in that case, is generally point- 

 ed, and the posterior end is gra- 

 dually extended into a long and 

 straight tail (fig. 329.). The latter 

 form is generally peculiar to the 

 singing birds, and, indeed, an ex- 

 clusive characteristic of them, en- 

 abling us, even by this circum- 

 stance, to detect the Picarii of 

 Nitzsch from the true birds of song. 

 Birds of the genera Coracias, Ca- 

 primulgus, Alcedo, at all events, 

 show this corkscrew form as little 

 as those of the genera Cuculus, 

 Picus, &c. ; whilst the birds of 

 the raven tribe exhibit this same 

 characteristic in common with the 

 singing birds. 



The number of separate twist- 

 ings or turnings of the body, and 

 their distance from each other, 

 is different, however, in the several 

 families and genera of singing birds. 

 Among the thrushes, for instance, the 

 spiral is very extended, and almost 

 undulating, whilst the numerous 

 twinings pass into one another at 

 an obtuse angle. The twistings 

 are less in number (from 4 to 5), 

 in the Lanius (the Shrike) ; they 

 are very narrow, and almost acute- 

 ly angular, whilst they are at a 

 greater distance from each other, 

 among the Finches, where their 

 number is still less (3 to 4). The 

 upper windings are, in most cases, 

 the most considerable, and likewise 

 the most constant, whilst the lower 

 become continually slighter, extend- 

 ing themselves sometimes (especi- 

 ally in Turdus, and likewise occa- 

 sionally in Fringilla) throughout 

 Sperma- the greatest part of the tail ex- 

 tozoonof tremitv of the spermatozoon. The 



fST kng* and thickness of the tail, 

 like the number and arrangement 



of the windings, is subject to many changes 

 and fluctuations among the several genera. 

 It is particularly strong and rigid among 

 the Fringillida3, the spermatozoa of which (as 

 in Fringilla coelebs, the Chaffinch) attain some- 

 times a length of "', whilst in other cases 

 they are much shorter (in Fr. Spinus = T V"> 

 F. Canaria T y", F. domestica ^"O- The tail 

 part of the spermatozoa of the LanidaB is, 

 on the other hand, very short and fine, 

 its length scarcely measures -fa'" '&/"> of 

 which about g^V" TO^ /// goes to the anterior 

 spiral body. The spermatozoa of Oriolus are 

 only slightly larger. Among the Thrushes'the 

 length is about -^ r ' y of which the anterior 

 spiral body occupies quite one third. The 

 same is the case among most other singing 

 birds, as Sturnus, Hirundo, Parus, Alauda, 

 Arthus, Certhia, &c. Motacilla and Emberza 

 have spermatozoa of -fa'", Sylvia (Phcenicurus 

 vibilatrix) and Saxicola of tV". Among the 

 last-mentioned genera, the spermatozoa form 

 by their shape a kind of approach to the cor- 

 responding formations of the Fringilla, whilst 

 the spermatozoa of others remind us more 

 of these formations in the thrushes and the 

 Lanidae. In other words, the formations 

 just alluded to form a medium between the 

 latter mentioned birds and the Fringilla. 



The spermatozoa with a simple cylin- 

 drical body are much more uniform in size 

 and shape, and differ from each other chiefly 

 as regards the length of the tail, very little as 

 to the length of the body. 



The body generally measures from Tio /x/ 

 2 i/" (Picus, Falco, Columba, Gallus, Pavo, 

 Anas, &c.), but seldom less (in Vanellus and 

 Cuculus = *&/"). The tail is very thin, 

 and can usually only be traced to its ter- 

 mination with difficulty. The anterior part, 

 which is connected with the body, is but 

 little distinguished from the posterior, and 

 is always without any remarkable thickening. 

 Its length is always more considerable than 

 the length of the body, the entire fibre gene- 

 rally measuring eV", and rarely less (Va- 

 nellus, Cuculus) or more (Gallus, Co- 

 lumba). 



It is an interesting fact that the difference 

 of form of the spermatozoa in birds is 

 associated with a difference in the man- 

 ner in which they adhere to each, other. 

 Those which have a simple cylindrical body, 

 are constantly dispersed about in the canals of 

 the testicles without any order, whilst the 

 spermatozoa of the singing birds are generally 

 met with in regular bundles. The spermatozoa 

 in each of these bundles, as in the mammalia, 

 lie together in paralleP lines, and with their 

 tails all in the same direction. It is only in 

 their passage through the vas deferens that the 

 bundles gradually lose their regular connexion. 



The genesis of the spermatozoa of birds, 

 is essentially the same as among the mam- 

 malia. Their proportions are, however, 

 much more distinct, and therefore more 

 easy to trace. The examination of the 

 domestic fowl is much to be recommended in 

 this respect ; some time ago we described 



