486 



SEMEN. 



windings, almost in the form of an S. 

 Fig. 357. 



Clausilia, &c.), it exhibits two easy spiral quently in an irregular manner, generally 



Some measure -I\Q"', but are sometimes larger, 

 to the extent of -rih/" an ^ above it. In 

 the interior of these cells we meet again 

 with vesicular formations, generally mea- 

 suring z-uo'"- The contents of these vesicles 

 coagulate on being treated with water, &c., 

 into a fine granular mass, exhibiting some- 

 times a simple or double granule of extra- 

 ordinary size. The number of the enclosed 

 vesicles, which evidently were produced in an 

 endogenous way, is usually very small, mostly 

 1 or 2, more rarely 3, 4, or 6. 



The developement of the spermatozoa takes 

 place in the interior of these last-men- 

 tioned vesicles (fig- 359.). According to the 



Fig. 359. 



Spermatozoon of Helix pomatia. 



easy spiral windings are also not unfrequently 

 observed at the enlarged body. 



The mode of formation of these sperma- 

 tozoa can usually be traced without any great 

 difficulty. It usually takes place in the same 

 way as in the animals already described, as 

 proved by Kollikcr''s excellent researches. Even 

 in the Gasteropods we may observe the deve- 

 lopement of the spermatozoa in the interior of 

 particular vesicles. The arrangement of these 

 parts only exhibits some deviation. 



In Helix or Clausilia, in which the stages of 

 this mode of developement can best be ob- 

 served amon<* our native snails, we meet with 

 in the interior of the testicle, besides the de- 

 veloped spermatozoa, numerous larger and 

 smaller aggregations of vesicles (in number 

 varying from ten to forty), which are seated 

 on the external surface of a round or oval 

 globule (fig. 358.), which is in diameter T ^ 5 - /// 

 to ^". 



On a nearer research, it will be found that 

 this globule is not a cell, as one might sup- 

 pose at first sight, but merely a mass of a 



Fig. 358. 



Group of vesicles from the testicle of Helix pomatia. 



tough substance, in which a number of small 

 brown granules are embedded, exhibiting a 

 great similarity with the yolk molecules from 

 the eggs of Helix. There is no external en- 

 closure around this globule. The periphe- 

 ral vesicles or cells, which adhere to it fre- 



Spermatozoon of Helix pomatia. in the interior of its 

 developing cell. (After Kolliher.) 



observations of Kolliker, the head is produced 

 first, being at first of a less regular, un- 

 wieldy shape. The tail is formed subse- 

 quently, attaching itself in spiral windings to 

 the internal surface of the cell wall. On the 

 spermatozoa being sufficiently developed, the 

 vesicle of developement is dissolved, and the 

 spermatozoa get into the cavity of the exter- 

 nal cell {fig. 360.). Here they may usually 



Fig. 360. 



Spermatozoa of Helix pomatia in the interior of 

 their mother cells. 



be perceived with great distinctness, whilst 

 they can but rarely be distinguished in the in- 

 terior of the real cells of developement. 



At first the mother cells retain their original 

 round form, even after the reception of the 

 spermatozoa. They soon, however, on the 

 windings of the fibres being stretched, extend 

 themselves lengthwise, and assume an ellipti- 

 cal or pyriform shape. At a still later period 

 the cell pushes forward (at the point where the 

 heads of the spermatozoa are situated) a long 

 pedicle-formed process, which contains the 

 anterior extremity of the spermatozoa (Jig. 

 361.). The point of this process or continu- 

 ation constantly remains connected with the 

 central globule of the former mass of vesi- 

 cles, whilst the posterior belly-like part of 

 the cell removes itself further and further from 

 it. The same attachment takes place after- 

 wards with the heads of the spermatozoa, on 

 their being projected from the anterior end of 

 this process, which usually happens soon. At 

 this period the mass of vesicles reminds us 



