INVEETEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 951 



female or hinder portion of the body there are two somewhat spacious 

 sacs, often found filled with zoosperms ; each of these communicates 

 with a narrow tubular canal, which opens into the ccelom by a ciliated 

 infundibulum. There is also another opening connected with these 

 sacs, the function of which is evidently that of a receptaculum seminis ; 

 these open to the exterior at the base of their proper paradopodia. 

 It is further to be noted that these sacs resemble in their structure 

 and arrangement segmental organs, and this is the more obvious in 

 young specimens in which the sexual products are still undeveloped. 

 The author is unable to decide definitely whether the male copulatory 

 organs are also to be regarded as modified segmental organs. 



Development and Classification of the Echiurida.* — Dr.Hatschek 

 has been fortunate enough to find a series of an Echiurid larva, of 

 which he gives an account. They were distinguished from the 

 species examined by Salensky not only by the fact that they were 

 considerably larger and exhibited a somewhat more complex develop- 

 ment of the organs, but also by the striking fact that they had not 

 one only, but two circlets of seta? at their hinder ends. 



The series exhibited a very marked increase in size, the specimens 

 being all within a month's development. 



The troclioplwre-stage includes all the phases of the unsegmented 

 animal. In this it is possible to detect all the parts which were 

 seen in the same stage in Poli/gordius ; there is no distinction 

 externally between the head and trunk, and the latter is, at this 

 period, very inconsiderable. In the cephalic region there is a 

 double-rowed pre-oral, and a single-rowed post-oral ciliary circlet, 

 while between them tbere is the adoral ciliated zone ; in addition to 

 this there is a ventral baud between the mouth and anus. This 

 region, later on, becomes deepened into the ventral (neural) groove. 

 At the interior pole of the body there is a transversely elongated 

 frontal plate, which is formed by a thickening of the ectoderm, and 

 is likewise ciliated. 



The limits of the cells of the ectoderm can only be distinguished 

 in some parts, and in the rest they have to be made out by the 

 arrangement of the nuclei. The mesodermal structures are thus 

 arranged. In the trunk, and lying close to the ectoderm, there are 

 very short mesodermal bands ; these commence by two large oval 

 cells placed just in front of the anus, and touching one another in the 

 middle line ; thoy are easily distinguished by their cleavagc-sphere- 

 like appearance. The few other cells of which the bunds are made 

 up are dillcrcnt in character, and are only arranged in double rows 

 quite anteriorly. 



The muscles iu the .cephalic region are altogether similar to those 

 seen in Puh/ijordius, and in addition to these we find on the wbole of 

 the inner surface of the body - wall a system of extrtmely fine 

 muscular filaments, which are closely attached to the ectoderm, and 

 are arrangcid partly in circular fashion and partly irr(>gulurly ; these 

 are shown, later on, to bo very characteristic of tlio Echiurid larva. 



* 'Clans' Arbeitcn,' iii. (1880) p. 45. 



