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Show 122 DR. J. S. BOWERBANK ON SPONGES. [Feb. 13, many cases all the four forms occur in different divisions of the same genus; and in some individuals, as in Isodictya varians (Mon. Brit. Spongiadse, vol. ii. p. 281), as many as three of the primary forms occur mixed in the skeleton; and in Lsodictya infundibuliformis (Mon. Brit. Spong. vol. ii. p. 317) we have the spicula of the primary lines of the skeleton attenuato-acuate, while those of the secondary lines are acerate, and in many other species we find acerate prevailing in number, but with a considerable admixture of acuate forms, thus totally ignoring the assumptions of Dr. Gray that the forms of the spicula are characteristic of the different families. Neither are " the many-rayed stellate, with rays on all sides, and the three-pronged or three-hooked elongate spicules characteristic of the Geodiadee and Tethyadee." Thus the sphero-stellate form occurs abundantly in Dictyocylindrus stuposus (Mon. Brit. Spongiadse, vol. ii. p. 116) and in many exotic species in no degree allied to either Geodia or Tethea, and ternate or " three-pronged " spicula are an essential part of the structure in some species of Dactylocalyx and other exotic genera. These are not the only crude and inaccurate assertions regarding the general structural characters of the spicula of sponges that are made by the author, but they are sufficient to illustrate the hasty style in which he arrives at his conclusions on these subjects. Page 499. Dr. Gray states the object of his proposed new system thus : - " I would propose the following arrangement as bringing together the species which seem most allied, and also as facilitating the study of these very difficult and anomalous animals." The author's generalizations in constructing his system are upon a wonderfully expansive scale. Thus his subclass Porifera silicea, p. 502, will include at least 99 per cent, of the whole number of known sponges, the calcareous ones as compared with the others being exceedingly few in number. The first step the author takes in his endeavours to simplify the arrangement of the sponges is to merge in one subclass the two very distinct divisions of Dr. Grant of Silicea and Keratosa ; and the unfortunate result is immediately visible in the same and following pages, 503 and 504, in bringing together groups the species of which are of the most varied and opposite anatomical structure; and the difficulty is increased by the author's descriptions of his orders immediately following, which are so vague and loosely put together as to be nearly incomprehensible, even to naturalists well acquainted with sponges. The first difficulty occurs in his description of section 1, page 502, "Malacosporee(Soi\-spored Sponges). Reproduction by ova contained in a thin membranaceous ovisac not strengthened by siliceous spicules or by gemmules scattered in the substance of the sponge." The author does not seem to be aware that it is comparatively a rare occurrence to find the description of gemmules to which he refers in situ, as they only occur thus at certain periods, and then for onlv a short time ; so that in thus making them the sole character of his section 1, Malacosporce, he is placing a complete stumblingblock in |