ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 837 



Dr. Packard calls the proventriculus corresponds to the " stomach " of 

 authors, the true stomach not being lined with chitine. How much of 

 the rectum is cast is uncertain, but the chitinous parts lying within 

 the body and serving as attachments for the muscles moving the caudal 

 spine, including two sets of slender tendon- like processes, are cast. 

 The gill-plates are also cast, as well as the delicate hair-like setas 

 fringing their edges. 



Moreover, and this is an interesting point, as in this respect the 

 moulted integument or shell of Limulus is like that of an Asaphus 

 the author examined, the seven pairs of apodemes or internal processes, 

 six pairs of which support the six pairs of abdominal feet, are also shed. 

 This similarity of form in the apodemes of Trilobites and Limulus 

 has been, to his mind, a strong argument for the existence in Trilo- 

 bites of membranous abdominal swimming feet like those of the 

 Limulus. 



A small specimen taken in the act of moulting, 50 mm. long 

 including the caudal spine and 30 mm. broad, was considerably larger 

 after casting its shell, measuring 65 mm. in length, and 40 mm. in 

 breadthj or about one-third larger. 



Vermes. 



Development of Annelids.* — W. Salensky has here three further 

 contributions to our knowledge of the developmental history of 

 Annelids. In the first he deals with a species of Pileolaria, allied to 

 P. militaris. The process of segmentation does not seem to resemble 

 either that of Psygmobranchus or that of Nereis, the multiplication of 

 the micromeres being effected either by division of the micromeres 

 themselves, or by their separation from the macromeres. At a com- 

 paratively early period, not only the dorsal and ventral surfaces, but 

 also the anterior and posterior ends may be distinguished ; the fore- 

 end has the ectoderm represented by a single set of cells, while the 

 region of the body is distinguished by the presence of the mesoderm. 

 At the boundary between these two regions there is a row of larger 

 ectodermal cells which, forming a zone, are longest on the ventral 

 surface ; they are the rudiments of the ciliary circlet. These ciliated 

 cells, when developed, are distinguished from the other ectodermal 

 cells by their size, their spherical form, and their structure ; within 

 each we see a finely granular protoplasmic body, which is thickened 

 at its periphery, and bears a tuft of cilia. This is the preoral circlet, 

 and the post-oral is not formed till later. As compared with Nereis 

 and others, Pileolaria seems to have a nervous system which is very 

 tardy in putting in an appearance ; the formation of the ganglionic 

 chain is preceded by the modification of the minute structure of the 

 ectoderm, which results in the formation of glandular elements and 

 of the ventral ganglionic chain in the more anterior regions. The 

 " individualization " of the endoderm which, in Psygmobranchus, leads 

 to the separation of that layer into two parts, does not obtain in 



* Arch. Biol., iv. (1883) pp. 143-264 (6 pis.). 



