488 



SEMEN. 



Spermatozoon, of Phalluria 

 monacha. (AfierKolliker. ) 



Tunicata. Among the Tunicata the Ascidia 

 possess spermatozoa quite similar to those of 



the Lamellibranchi- 

 Fig. 365. ates, having a dis- 



tinct head of dif- 

 erent shape and a 

 slender tail. The 

 size of the sperma- 

 tozoa is, however, 

 usually rather larger 

 (fig. 365.); the head 

 is usually ji^'" 

 i-s", the tail fluctu- 

 ating between gV 

 i,V'" The sper- 

 matozoa seem to 

 want a body in the 

 Salpae, according to 

 the observations of 

 KoUtker. 



The endogenous 

 formation of the 



spermatozoa in the Ascidia is as little distinct 

 as among the Lamellibranchiata. It seems, also, 

 with regard to the former, that the developing 

 vesicles simply extend themselves into the 

 spermatozoa. At a previous stage of deve- 

 lopement, these vesicles are, however, con- 

 tained (either singly or in a greater number) 

 in the interior of cells. 



ARTICULATA. In the second great division 

 of the Invertebrate animals, among the Artliro- 

 pocla, the filiform shape of the spermatozoa, if 

 indeed it occurs at all, is generally still more 

 marked in its developement than in the 

 Mollusca. The spermatozoa are long and 

 slender fibres, which, perhaps in all cases, are 

 deficient of a real, distinct, and separate body, 

 being at the utmost only slightly enlarged at the 

 anterior end. The spermatozoa of some few 

 groups, however, differ from this, and ex- 

 hibit so striking a form and arrangement that 

 one can hardly at first recognise in them the 

 genuine spermatic elements. The question, 

 indeed, arises, whether these parts are really 

 in all cases the developed spermatozoa, or 

 whether they do not constitute mere stages of 

 developement. We shall subsequently return 

 to this question ; let the remark suffice for the 

 present, that in some cases the circumstances 

 observed seem to favour the latter hypothesis. 

 Insecta. The spermatozoa among the hexa- 

 pod insects are of great uniformity. They ap- 

 pear, without exception, as filiform fibres (Jig. 

 366.), which are frequently distinguished by 

 being extremely slender in proportion to their 

 length (the latter exceeds I"' in Staphylinus, 

 but is generally less ; in Culex $'"; in Agrion 

 Virgo 6*0"' sTr'")' The anterior end is pro- 

 bably always rather thickened for a consider- 

 able extent, and thereby distinguished from the 

 posterior pointed end of the fibre. Remark- 

 able deviations from this fundamental shape 

 occur but rarely, but are nevertheless not en- 

 tirely wanting. We may mention, for instance, 

 that a peculiar angular appendix is found in 

 the spermatozoa of the Locustina? at the an- 

 terior end of the body, this appendix being 

 formed of two short crura, which 



and pass into one towards the anterior part, 

 like the head of an arrow. 



Fig. 366. 



Spermatozoa of an Insect. 



The spermatozoa of the Hexapods are 

 developed in the same endogenous man- 

 ner, as among the Vertebrata. This process 

 ma}' very easily be observed. The vesicles of 

 developement, which measure pretty uniformly, 

 when in a developed state, ^- '" (they are 

 smaller in many Diptera, Culex C^^'"), Musca, 



Fig. 367. 



Cysts, with clcrc/ojiinr/ i-csicles, from the testicle oj 

 Staphylinus cyaneus. 



&c.), are in a variable, generally, however, 

 in considerable number (twenty, thirty, 

 forty), enve'oped by larger cysts (,fig- 367.) 

 These cysts or enveloping cells frequently 

 attain the size of ^L"' (Carabus, Staphy- 

 linus, Locusta, &c.), and they are evidently 

 the mother cells of the enclosed vesicles. 

 In the upper division of the testicle, the 



