ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 49 



wider geographical distribution being in most instances coincident 

 with the shallower depths." 



To this law another striking exception is afforded by the beautiful 

 genus Gntenicella, a genus very rich in species, which, though from 

 comparatively shallow water, are almost exclusively confined to the 

 Australian region.* 



y. BracMopoda. 



Argiope Kowalevskii.t — M. A. Schulgin finds that the essential 

 part of the internal skeleton — the brachial framework, to which, in 

 most Terebratulids, the gills are attached, is wanting in Argiope. The 

 lower part is alone present, and forms a ramus basilaris to which 

 the lower end of the tentacular disk is attached. The shell is laid 

 down over the whole extent of its surface, and is not a derivate of a 

 gland as in the Mollusca. The tentacular disk is not a special 

 respiratory organ, but a mere thickening of the mantle, and its long 

 tubules are nothing more than tentacles ; respiration is effected at all 

 points of the body, and especially by means of the pallial outgrowths 

 which traverse the shell and reach to the exterior. There is no heart 

 nor any specially formed vessels ; the blood is set in motion by the 

 ciliated epithelium of the peritoneal cavity into which there open the 

 blood-carrying lacunae. 



The nervous system consists of a feebly developed sub-oesophageal 

 ganglion, a thin nerve-ring, and strongly developed peripheral 

 branches. The tactile organs have the forms of high cells, and are 

 found at the margin of the mantle ; there is a special organ in the 

 integument near the mouth. The author finds ten, but Kowalevsky 

 describes only eight muscles ; the former finds no basis for a com- 

 parison, such as that instituted by the latter, between these muscles and 

 those of anneKds. Although the embryos of Argiope have segments, 

 yet the muscles and dissepiments of annelids are not represented. 

 Semper's statement that the mesoderm takes no share in the formation 

 of the segments is confirmed ; it follows that the muscles have a 

 diiferent developmental history. Similarly, the set^e are not to be 

 regarded as homologous, for similar structures are developed in 

 Chitons and other molluscs ; and these setae are not on the "segments" 

 but on the lobe (the future mantle), which has nothing to do with the 

 segment. 



The only organs which are both homologous and analogous are 

 the brood pouch of Argiope and the segmental organs of adult 

 annelids ; a similar organ is found in PedicelUna. This form 

 resembles Argiope in having the central nervous organ similar in 

 position, its lophophor appears to be the homologue of the tentacular 

 disk. It is probable that the Polyzoa and Brachiopoda arose from a 

 side branch of a phylum which also gave rise to Annelids, and they 

 may be separated from the Molluscoidea, and grouped together under 

 the class of Vermoidea. 



The author's essay was completed before the publication of Mr. 



* Dr. G. J. Allman in ' Nature.' xxxi. (1884) pp. 146-7. 

 t Zeitschr. f. Wiss. Zool., xli. (1884) pp. 116-41 (2 pis.). 

 Ser. 2^.— Vol. V. E 



