SEA-FIR. 249 



Under these circumstances they go through active migrations. In Sertularia 

 pumila the generative zooid is a reduced medusoid gonophore ; the ova arise in the 

 endoderm (? from wandering ectoderm cells) of the branch or stem below the spot 

 from which the gonangial bud springs, wander through the endoderm of the blasto- 

 style and gonophore, pierce the supporting lamella, and ripen in the ectoderm of the 

 gonophore. The generative zooid of ,5". abietina requires investigation. 



Hydrozoa, Ray Lankester, Encyclopaedia Brit. (ed. ix.) xii. British Hydroid 

 Zoophytes, Hincks, 2 vols. 1868. Gymnobtastic Hydroids, Allman, Ray Soc. 1871. 

 Id. Hydrozoa, pt. i, Plumularidae, Challenger Reports, vii. 1883. Organismus 

 der Hydreidpolypen, Hamann, J. Z. xv. 1882. System, &C. der Medusen, Haeckel, 

 Dk. Med. Natwiss. Gesellsch. Jena, i. 1879 ; ii. 1881 ; Id. Challenger Reports, iv. 

 1882. Organismus der Medusen, Hertwig (O. and R.), Jena, 1878. lid. Nerven- 

 system und Sinnesorgane der Medusen, Leipzig, 1878. Helgolander Leptomedusen, 

 Bohm, J. Z. xii. 1878. 



Cordylophora lacustris, Schulze, Leipzig, 1871. Syncoryne Sarsii and Sarsia 

 tttbulosa, Id. Leipzig, 1873. Tubularia, Ciamician, Z. W. Z. xxxii. 1879; cf. 

 Conn, Johns Hopkins Univ. Circulars, No. 17, 1882. Eudendrium, Jickeli, M. J. 

 viii. 1882. Limnocodium, Bourne, P. R. S. xxxviii. 1884-85 ; Nature, xxxi. 1884-85 ; 

 Ray Lankester, Q. J. M. xx. 1880; Allman, J. L. S. xv. 18.81. Campanularia 

 angulata, Fraipont, A. Z. Expt. viii. 1880. Eucopella Campanularia, von Lenden- 

 feld, Z. W. Z. xxxviii. 1883. Clytia Johnstoni, Klaatsch, M. J. ix. 1884. Medusa 

 of Obelia, Merejkowski, Bull. Soc. Zool. France, viii. 1883. 



Nervous system in Hydroid polypes. Jickeli, op. cit. supra. In Siphonophora, 

 Chun, Z. A. iv. 1881 ; v. 1882 ; Korotneff, Z. A. v. 1882 ; Conn and Beyer, Johns 

 Hopkins Biol. Studies, ii. 1883. Physiology. Romanes, Jelly-fish, Star-fish, and 

 Sea-urchins, Internal. Series, 1. 1885. 



Intracellular digestion. Metschnikoff, Arb. Zool. Inst. Wien, v. 1883, transl, 

 Q. J. M. xxiv. 1884; Ray Lankester, Q. J. M. xxi. 1881 ; Krukenberg, Vergleich. 

 Physiol. Studien (2), Abth. ii. p. 139. 



Water in umbrella of Medusae. Krukenberg, Z. A. iii. 1880 ; Mobius, Z. A. 

 v. 1882. 



Sexual cells, origin, 6<r. Weismann, Sexual-zellen (male and female) bei 

 Hydromedusen, Jena, 1883; cf. Moseley, Nature, xxix. 1883-84: de Varenne, 

 A. Z. Expt. x. 1882; cf. Bourne, Q. J. M. xxiii. 1883. Female celL. Hartlaub, 

 Z. W. Z. xii. 1884. Male cell. Thallwitz, J. Z. xviiL 1885. 



51. FRESH-WATER SPONGE (Spongilla lacustris), 



From the Isis, growing on the wall of a lock, with Figure 12, illustrating the structure of 



Euspongia ojKcinalis. 



THIS specimen, like the preceding Hydroid (Prep. 50), is plant-like in 

 appearance, consisting, as it does, of a base of attachment and two upright 

 stems arising close together. Spongilla lacttstris often attains a large size. 

 Owing to its having been preserved in spirit, this specimen has the surface 

 more fenestrated than in the living condition ; its protrusible oscula or 



