THE ANIMAL KINGDOM. 



situated on the wall of the sac, close to the outer opening (Aspidosiphon 

 fuscus, several species of Sipunculus including 5. mtdus, Phascolion Strombi) ; 

 or near its apex (Siptmculus editlis, Phascolosoma nigritorquatiis^ Ph. 

 falcidentatus), and are either funnel-shaped or bilobed. They are always 

 anterior, near the external aperture in EcJmiridae, and are either simple 

 funnels (Bonellia, Hamingia ?), bilabiate funnels (Echiurus Pallasii, Tha- 

 lassema Neptuni) &c.), or they are drawn out on each side into a long 

 gutter, which is twisted into a spiral (Echiurus unicinctus, many species of 

 Thalassema). The funnels are ciliated in the Echiuridae^ and there can be 

 little doubt that such is the case in Sipunculidae also. The homology 

 of these organs with nephridia is undoubted, but it is by no means a settled 

 fact that they are excretory in function. 



The sexes are said to be separate, and are undoubtedly so in most 

 cases, the possible exceptions being among Sipuncididae \ The genital 

 organs of the Priapulidae consist of two ducts, one right, the other left, 

 opening posteriorly near the anus, and attached by a ventral mesentery to 

 the body- walls. The lobulated genital gland lies on either side this 

 mesentery in the female, but nearly surrounds the duct in the male. The 

 main duct gives off lateral branches which divide repeatedly, and in the 

 female anastomose. The ova take their origin from isolated cells of the 

 epithelium, which grow at the cost of their neighbours ; the sperm from 

 the epithelium at the base of short caeca appended to the canals. In all 

 other Gephyreans the genital products are found floating in the coelome. 

 In the Sipunculidae little is really ascertained as to the genital glands. In 

 Sipunculus edulis and Phascolosoma nigritorquatus the ovaries are small 

 sausage-shaped bodies, placed in a row between the dorsal retractor muscles 

 of the pharynx, attached to them and to the alimentary canal. They 

 consist of fibrous sacs, which are eventually burst by the growing cells 

 they contain. The testes are not known. In Aspidosiphon fuscus both 

 ovaries and testes have the form of mesenterial folds attached behind the 

 ventral retractors of the pharynx on either side the nerve cord, between two 

 bundles of circular muscles. The ova are detached, and ripen in the 

 coelome ; the sperm is formed in situ, and then detached. In Phascolosoma 

 falcidentatus the ovaries are similar to those of Aspidosiphon^ similarly 

 placed, but attached between the longitudinal muscles. Its testes are not 

 known. As a rule, the ova and the cells from which the sperm originates, 

 are set free at an early period into the coelome, hence ' swimming ovaries 



1 Sperm and ova may alike be found floating in the coelome of Sipunculus mtdus, but 

 according to Brandt, most individuals of this species contain either ova or sperm. The simultaneous 

 presence of both products he explains as possibly due to an abnormality, unless it be supposed that 

 the animal is hermaphrodite, and that the two products ripen as a rule at different times, but occasionally 

 at the same time. A Gregarine, Monocystis Sipunculi, is not uncommon in the coelome of the 

 species in question. A Gregarine occurs also in Echiurus Pallasii and Thalassema Neptuni. 



