1040 Annelides. 



body, the mammse are found opposed to each other at the ends of the cocoon. The 

 sinus is produced by a partial state of collapse of the body of the cocoon, caused ap- 

 parently by the gradual diminution of its gelatinous contents. The cocoon in almost 

 every specimen that I have opened, was found to contain a dense opaline gelatinous 

 matter. When removed it readily separates in water into flaky masses, which, when 

 viewed by transmitted light, with a power of 500 linear, appeared to be composed of 

 exceedingly minute granules. Upon carefully examining the gelatinous contents of 

 several specimens which I opened, I found in two of them small vesicular bodies, 

 which have every appearance of being the eggs or embryos of the animal. In the ge- 

 latinous matter of one specimen I found ten of these bodies, and in another six of 

 them, apparently in different stages of development. They are usually pyriform, and 

 have frequently a deposit of minute, dark, granulated matter towards the smaller end. 

 In both cases in which these bodies occurred, they were found in greater quantities at 

 one end of the cocoon than at the other. The network which covers the outer surface 

 of the body of the cocoon and bounds the deeply sunken areas of its interstices, rises 

 from its surface in the form of a sharp edge, and as the free fibres are given off at 

 the angles where the imbedded fibres meet, they naturally at this point assume 

 the form of a three-winged fibre, and this form they maintain throughout the whole 

 of their length. Every one is familiar with the horny cases surrounding the ova of 

 certain fishes, and of the finely-spun horny threads with which they are fixed to the 

 stems of Gorgonias and other bodies ; but in these cases the fibre is simple and cylin- 

 drical, as might naturally be expected, while in the fibrous tissue of this singular co- 

 coon it is three-winged, and anastomoses as regularly and as beautifully as the fibres 

 of the horny sponges of commerce. How the animal produces this beautiful and com- 

 plex structure, is a question which it will be exceedingly interesting hereafter to solve. 

 The coriaceous substance of the body is of about the thickness of a stout sheet of writ- 

 ing-paper, the centres of the areas being much thinner than the other parts. When a 

 section of one of its thickest portions at right angles to its outer surface was examined 

 by transmitted light with a power of 94 linear, it appeared to be composed of four or 

 five layers of nearly equal thickness. When the exterior surface was examined under 

 similar circumstances, with a power of 1 000 linear, numerous cytoblastic vesicles were 

 observed irregularly dispersed over its surface, but without the appearance of nuclei ; 

 but, on the contrary, when the inner surface was thus examined, it was seen to be 

 nearly uniformly covered with well-defined nucleated cytoblasts, the nuclei in many 

 cases being angular. From the laminated structure exhibited, it is probable that the 

 production of tessellated cellular tissue is not continuous, but that it occurs at inter- 

 vals, and is produced by a series of efforts, in a similar manner to that in which the 

 successive layers of cartilaginous substance are produced by Helix aspersa when about 

 to extend the lip of its shell in the spring of the year. But there is an essential dif- 

 ference in the circumstances of the two cases. In the shell the cytoblasts are deve- 

 loped and their peculiar office performed while in contact with the living body whence 

 they emanate, while in the cocoon this cannot well be the case, as the animal immedi- 

 ately separates itself from it. Their presence and development therefore appear to indi- 

 cate that vitality to a certain degree remains in the horny substance of the cocoon, and 

 which vitality may probably continue in action until the proper office of the cocoon 

 has been attained. Dr. Johnson, in treating of Hirudo vulgaris, describes the singu- 

 lar mode of the production of the cocoon of that species in this manner. When the 

 animal is about to produce one of these bodies, it is observed to be greatly contracted 



