ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 359 



substance ; and this remark applies even to the " stalk." The compli- 

 cated lacunar system, described by Hancock, would appear to be 

 merely due to the mode of connection of the stellate connective-tissue 

 cells ; and this is the more probable as an explanation, since Hancock, 

 in his very careful account, never mentions the connective-tissue 

 elements. To the author just mentioned we owe our first exact know- 

 ledge of the nervous system of this group. On either side, the wall 

 of the pharynx gives rise to a fold which carries the cesophageal 

 ring ; below the pharynx is the ventral ganglion, in which we lind 

 two continuous lateral aggregations of ganglionic cells, connected with 

 one another by nerve-fibres. From this there is given off, on either 

 side, a thick nerve which at once divides into two branches ; one 

 of these, the thicker, passes to the dorsal half of the mantle, the other 

 (and thinner) to the commissure. The lateral commissures curve over 

 in front of the pharynx, towards the body-wall, and thence pass into 

 a nerve-cord, which extends into the walls of the arms and expands, 

 above the mouth, into a ganglion. It follows, therefore, that there are 

 supra-oesophageal arm-nerves, and these are much larger than the 

 sub-oesophageal. After describing the minute structure of the parts 

 of the nervous system, the author passes to the genital organs. 



Here, again, we find the remarkable researches of Hancock duly 

 noted ; but the more modern author has been able to make out that 

 there is no sharp distinction between the epithelium of the body- 

 cavity and the ovarian cells ; and that, therefore, the ova of the 

 Brachiopoda may be said to be metamorphosed coBlomic cells. It 

 is true also of the spermatozoa that they arise from a germinal 

 epithelium which is directly continuous with the epithelium of the 

 body-cavity. This coelom is lined by a single layer of flattened 

 epithelial cells, and the genital glands are placed in folds of the sup- 

 porting substance, in which cavities are developed. It seems certain 

 that the Brachiopoda Testicardinia have the sexes separate. 



The muscles consist of parallel simple fibres of contractile sub- 

 stance, which for the most part are not connected together, and which 

 apparently extend through the length of the whole muscle. Nuclei are 

 to be found on their outer side, and these are surrounded by a very 

 small amount of granular protoplasm. The only difference between 

 the plain and striated muscles is to be seen in the structure of the 

 latter. 



Coming to the discussion of the systematic position of these 

 difficult forms, the author finds that, in the histological structure of 

 their body- wall, musculature, and genital organs, they present all the 

 characters of the Enterocoelia of the Hertwigs ; the mesenchymatous 

 layer is but feebly developed. 



Instead of being allied to the MoUusca, they appear to present the 

 closest resemblance to the Chfetognatha. Not only do the ectoderm, 

 the enteric canal, and the body-cavity present just the same develop- 

 mental history, but in both we observe a feeble development of connec- 

 tive tissue ; the only differentiation in this layer is the formation of 

 supporting fibres. Further, we find that epithelia are always simple, 

 and the generative products are directly produced from one of them 



